ST20-GP1 [STMICROELECTRONICS]
GPS PROCESSOR; GPS处理器
| 型号： | ST20-GP1 |
| 厂家： | 
ST |
| 描述： | GPS PROCESSOR |
| 文件： | 总116页 (文件大小：881K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
ST20-GP1
GPS PROCESSOR
ENGINEERING DATA
FEATURES
■ Application specific features
• 12 channel GPS correlation DSP hardware
and ST20 CPU (for control and position calu-
culations) on one chip
GPS
radio
• no TCXO required
• RTCA-SC159 / WAAS / EGNOS supported
ST20-GP1
■ GPS performance
• accuracy
- stand alone
with SA on <100m, SA off <30m
- differential <1m
- surveying <1cm
• time to first fix
- autonomous start 90s
- cold start 45s
12 channel GPS
hardware DSP
ST20
CPU
- warm start 7s
Low
power
controller
Interrupt
controller
- obscuration 1s
■ 32-bit ST20 CPU
• 16/33 MHz processor clock
• 25 MIPS at 33 MHz
Real time
clock/calendar
Serial
• fast integer/bit operations
■ 4 Kbytes on-chip SRAM
• 130 Mbytes/s maximum bandwidth
■ Programmable memory interface
• 4 separately configurable regions
• 8/16-bits wide
• support for mixed memory
• 2 cycle external access
■ Serial communications
• Programmable UART (ASC)
• OS-Link
communications
2 UART (ASC)
1 OS-Link
4K
SRAM
.
.
.
Parallel
input/output
6
8
Programmable
memory
.
.
.
Byte-wide
parallel port
interface
■ Vectored interrupt subsystem
• 2 dedicated interrupt pins
• 5 levels of interrupt
■ Power management
ROM/
FLASH
RAM
• low power operation
• power down modes
■ Professional toolset support
• ANSI C compiler and libraries
• INQUEST advanced debugging tools
■ Technology
• Static clocked 50 MHz design
• 3.3 V, sub micron technology
■ 100 pin PQFP package
APPLICATIONS
■ Global Positioning System (GPS) receivers
■ Car navigation systems
■ Fleet management systems
■ Time reference for telecom systems
October 1996
1/116
42 1672 02
The information in this datasheet is subject to change
Contents
1
2
3
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
ST20-GP1 architecture overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Digital signal processing module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1
DSP module registers .......................................................................................................................... 13
4
Central processing unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.1
4.2
4.3
4.4
4.5
4.6
Registers .............................................................................................................................................. 18
Processes and concurrency ................................................................................................................ 19
Priority .................................................................................................................................................. 21
Process communications ..................................................................................................................... 21
Timers .................................................................................................................................................. 22
Traps and exceptions .......................................................................................................................... 23
5
Interrupt controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.1
5.2
5.3
5.4
5.5
5.6
Interrupt vector table ............................................................................................................................ 29
Interrupt handlers ................................................................................................................................. 29
Interrupt latency ................................................................................................................................... 30
Pre-emption and interrupt priority ........................................................................................................ 30
Restrictions on interrupt handlers ........................................................................................................ 30
Interrupt configuration registers ........................................................................................................... 31
6
7
Instruction set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.1
6.2
6.3
Instruction cycles ................................................................................................................................. 34
Instruction characteristics .................................................................................................................... 35
Instruction set tables ............................................................................................................................ 36
Memory map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
7.1
7.2
7.3
System memory use ............................................................................................................................ 45
Boot ROM ............................................................................................................................................ 46
Internal peripheral space ..................................................................................................................... 46
8
9
Memory subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
8.1
SRAM .................................................................................................................................................. 49
Programmable memory interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9.1
9.2
9.3
EMI signal descriptions ........................................................................................................................ 51
Strobe allocation .................................................................................................................................. 52
External accesses ................................................................................................................................ 52
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ST20-GP1
9.4
9.5
9.6
MemWait .............................................................................................................................................. 56
EMI configuration registers .................................................................................................................. 58
Reset and bootstrap behavior .............................................................................................................. 59
10 Clocks and low power controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
10.1
10.2
10.3
10.4
Clocks .................................................................................................................................................. 61
Low power control ................................................................................................................................ 61
Low power configuration registers ....................................................................................................... 63
Clocking sources ................................................................................................................................. 65
11 System services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
11.1
11.2
Reset, initialization and debug ............................................................................................................. 67
Bootstrap ............................................................................................................................................. 68
12 Serial link interface (OS-Link) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
12.1
12.2
12.3
OS-Link protocol .................................................................................................................................. 70
OS-Link speed ..................................................................................................................................... 70
OS-Link connections ............................................................................................................................ 71
13 UART interface (ASC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
13.1
13.2
13.3
13.4
13.5
Asynchronous serial controller operation ............................................................................................. 73
Hardware error detection capabilities .................................................................................................. 76
Baud rate generation ........................................................................................................................... 76
Interrupt control .................................................................................................................................... 77
ASC configuration registers ................................................................................................................. 79
14 Parallel input/output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
14.1
PIO Port ............................................................................................................................................... 85
15 Byte-wide parallel port . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
15.1
15.2
15.3
15.4
EMI mode operation ............................................................................................................................ 88
Parallel link (DMA) mode operation ..................................................................................................... 88
Configuration registers ......................................................................................................................... 88
External data transfer protocols ........................................................................................................... 89
16 Configuration register addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
17 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
18 GPS Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
18.1
18.2
Accuracy ............................................................................................................................................ 100
Time to first fix ................................................................................................................................... 101
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ST20-GP1
19 Timing specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
19.1
19.2
19.3
19.4
19.5
EMI timings ........................................................................................................................................ 102
Link timings ........................................................................................................................................ 104
Reset and Analyse timings ................................................................................................................ 105
ClockIn timings .................................................................................................................................. 106
Parallel port timings ........................................................................................................................... 107
20 Pin list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110
21 Package specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
21.1
21.2
ST20-GP1 package pinout ................................................................................................................ 112
100 pin PQFP package dimensions .................................................................................................. 113
22 Device ID . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
23 Ordering information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
4/116
ST20-GP1
1 Introduction
The ST20-GP1 is an application-specific single chip micro using the ST20 CPU with
microprocessor style peripherals added on-chip. It incorporates DSP hardware for processing the
signals from GPS (Global Positioning System) satellites.
The twelve channel GPS correlation DSP hardware is designed to handle twelve satellites, two of
which can be initialized to support the RTCA-SC159 specification for WAAS (Wide Area
Augmentation Service) and EGNOS (European Geostationary Navigation Overlay System)
services.
The ST20-GP1 has been designed to minimize system costs and reduce the complexity of GPS
systems. It offers all hardware DSP and microprocessor functions on one chip. Whilst the entire
analogue section, RF and clock generation are available on a companion chip. Thus, with the
addition of a ROM and a RAM chip, a complete GPS system is possible using just four chips, see
Figure 1.1.
Antenna
ST20-GP1
DSP
ASIC
Driver
(optional)
Radio
UART
CPU
Single chip
Parallel I/O
Low
cost
crystal
Real
time
clock
Watchdog
timer
No TCXO
ROM
RAM
Figure 1.1 GPS system
The ST20-GP1 supports large values of frequency offset, allowing the use of a very low cost
oscillator, thus saving the cost of a Temperature Controlled Crystal Oscillator (TCXO).
The CPU and software have access to the part-processed signal to enable accelerated acquisition
time.
The ST20-GP1 can implement the GPS digital signal processing algorithms using less than 50% of
the available CPU processing power. This leaves the rest available for integrating OEM application
functions such as route-finding, map display and telemetry. A hardware microkernel in the ST20
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ST20-GP1
CPU supports the sharing of CPU time between applications without an operating system or
executive overhead.
The architecture is based on the ST20 CPU core and supporting macrocells developed by SGS-
THOMSON Microelectronics. The ST20 micro-core family provides the tools and building blocks to
enable the development of highly integrated application specific 32-bit devices at the lowest cost
and fastest time to market. The ST20 macrocell library includes the ST20Cx family of 32-bit VL-
RISC (variable length reduced instruction set computer) micro-cores, embedded memories,
standard peripherals, I/O, controllers and ASICs.
The ST20-GP1 uses the ST20 macrocell library to provide the hardware modules required in a
GPS system. These include:
•
•
•
•
•
•
DSP hardware
Dual channel UART for serial communications
6 bits of parallel I/O
Interrupt controller
Real time clock/calendar
Watchdog timer
The ST20-GP1 is supported by a range of software and hardware development tools for PC and
UNIX hosts including an ANSI-C ST20 software toolset and the ST20 INQUEST window based
debugging toolkit.
6/116
ST20-GP1
2 ST20-GP1 architecture overview
The ST20-GP1 consists of an ST20 CPU plus application specific DSP hardware for handling GPS
signals, plus a dual channel UART, 8-bit parallel half-duplex link interface, 6-bit parallel IO, real time
clock and watchdog functions.
Figure 2.1 shows the subsystem modules that comprise the ST20-GP1. These modules are
outlined below and more detailed information is given in the following chapters.
DSP
The ST20-GP1 includes DSP hardware for processing signals from the GPS satellites. The DSP
module generates the pseudo-random noise (prn) signals, and de-spreads the incoming signal.
It consists of a down conversion stage that takes the 4 MHz input signal down to nominally zero
frequency both in-phase and quadrature (I & Q). This is followed by 12 parallel hardware channels
for satellite tracking, whose output is passed to the CPU for further software processing at a
programmable interval, nominally every millisecond.
CPU
The Central Processing Unit (CPU) on the ST20-GP1 is the ST20 32-bit processor core. It contains
instruction processing logic, instruction and data pointers, and an operand register. It directly
accesses the high speed on-chip memory, which can store data or programs. The processor can
access up to 4 Mbytes of memory via the programmable memory interface.
7/116
ST20-GP1
GPS
radio
ST20-GP1
12 channel GPS
hardware DSP
ST20
CPU
Serial
communications
Interrupt
controller
Interrupts
OS-Link
User position
2 UART
1 OS-Link
output in
ASCII
Low
power
controller
.
.
.
Parallel
input/output
6
8
Real time
clock
Byte-wide
parallel
port
.
.
.
4K
SRAM
Reset
System
services
Analyse
Error
Programmable
memory
Clock
interface
ROM/
FLASH
RAM
Figure 2.1 ST20-GP1 architectural block diagram
8/116
ST20-GP1
Memory subsystem
The ST20-GP1 on-chip memory system provides 130 Mbytes/s internal data bandwidth,
supporting pipelined 2-cycle internal memory access at 30 ns cycle times. The ST20-GP1 memory
system consists of SRAM and a programmable memory interface. The programmable memory
interface is also referred to as an external memory interface (EMI).
The ST20-GP1 uses 8 or 16-bit external RAM, 8 or 16-bit ROM, and supports an address width of
20 bits.
The ST20-GP1 product has 4 Kbytes of on-chip SRAM. The advantage of this is the ability to store
time critical code on chip, for instance interrupt routines, software kernels or device drivers, and
even frequently used data.
The ST20-GP1 memory interface controls the movement of data between the ST20-GP1 and off-
chip memory. It is designed to support memory subsystems without any external support logic and
is programmable to support a wide range of memory types. Memory is divided into 4 banks which
can each have different memory characteristics and each bank can access up to 1 Mbyte of
external memory.
The normal memory provision in a simple GPS receiver is a single 128K x 8-bit SRAM (55 or 70 ns
access time), and a single 64K x 16-bit ROM or Flash ROM (70, 90 or 100 ns access time). The
ST20-GP1 can support up to 1 Mbyte of SRAM plus 1 Mbyte of ROM, enabling additional
applications to be loaded if required.
Low power controller, real time clock and watchdog timer
The ST20-GP1 has power-down capabilities configurable in software. When powered down, a
timer can be used as an alarm, re-activating the CPU after a programmed delay. This is suitable for
ultra low power or solar powered applications such as container tracking, railway truck tracking, or
marine navigation buoys that must check they are on station at intervals. The timer can also be
used to provide a watchdog function, resetting the system if it times out.
The real time clock/calendar function is provided by a 64-bit binary counter running continuously
from the low-power clock (nominally 32768 Hz).
The ST20-GP1 is designed for 0.5 micron, 3.3 V CMOS technology and runs at speeds of up to
33 MHz. 3.3 V operation provides reduced power consumption internally and allows the use of low
power peripherals. In addition, a power-down mode is available on the ST20-GP1.
The different power levels of the ST20-GP1 are listed below.
•
•
Operating power — power consumed during functional operation.
Stand-by power — power consumed during little or no activity. The CPU is idle but ready to
immediately respond to an interrupt/reschedule.
•
Power-down — clocks are stopped and power consumption is significantly reduced. Func-
tional operation is stalled. Normal functional operation can be resumed from previous state
as soon as the clocks are stable. No information is lost during power down as all internal
logic is static.
•
Power to most of the chip removed — only the real time clock supply (RTCVDD) power on.
In power-down mode the processor and all peripherals are stopped, including the external memory
controller and optionally the PLL. Effectively the internal clock is stopped and functional operation
is stalled. On restart the clock is restarted and the chip resumes normal functional operation.
9/116
ST20-GP1
Serial communications
The ST20-GP1 has two UARTs (Asynchronous Serial Controllers (ASCs)) for serial
communication. The UARTs provide an asynchronous serial interface and can be programmed to
support a range of baud rates and data formats, for example, data size, stop bits and parity.
There is one OS-Link on the ST20-GP1 which acts as a DMA engine independent of the CPU. The
OS-Link uses an asynchronous bit-serial (byte-stream) protocol, each bit received is sampled five
times, hence the term oversampled link (OS-Link). The OS-Link provides a pair of channels, one
input and one output channel. The link is used for:
•
•
•
bootstrapping during development,
debugging,
communicating with OS-Link peripherals or other ST20 devices.
Interrupt subsystem
The ST20-GP1 interrupt subsystem supports five prioritized interrupts. Three interrupts are
connected to on-chip peripherals (2 for the UARTs, 1 for the programmable IO) and two are
available as external interrupt pins.
All interrupts are at a higher priority than the high priority process queue. Each interrupt level has a
higher priority than the previous and each level supports only one software handler process.
Note that interrupt handlers must not prevent the GPS DSP data traffic from being handled. During
continuous operation this has 1 ms latency and is not a problem, but during initial acquisition it has
a 32 µs rate and thus all interrupts must be disabled except if used to stop GPS operation.
Byte-wide parallel port
The byte-wide parallel port is provided to communicate with an external device. It transfers a byte
at a time, operating half duplex in the program-selected direction.
Parallel IO module
Six bits of parallel IO are provided. Each bit is programmable as an output or an input. Edge
detection logic is provided which can generate an interrupt on any change of an input bit.
System services module
The ST20-GP1 system services module includes:
•
•
reset, initialization and error port.
phase locked loop (PLL) — accepts 16.368 MHz input and generates all the internal high
frequency clocks needed for the CPU and the OS-Link.
10/116
ST20-GP1
3 Digital signal processing module
The ST20-GP1 chip includes 12 channel GPS correlation DSP hardware. It is designed to handle
twelve satellites, two of which can be initialized to support the RTCA-SC159 specification.
The digital signal processing (DSP) module extracts GPS data from the incoming IF (Intermediate
Frequency) data. There are a number of stages of processing involved; these are summarized
below and in Figure 3.1. After the 12 pairs of hardware correlators, the data for all channels are
time division multiplexed onto the appropriate internal buses (i.e. values for each channel are
passed in sequence, for example: I , Q , I , Q ... I , Q , I , Q ).
1
1
2
2
12
12
1
1
I correlator
(x 12)
DMA
interface
4 MHz IF
input
frequency
converter B
frequency
converter A
accumulator
Q correlator
(x 12)
data
sampler
Pseudo random
noise sequence
generator
Numerically
controlled
oscillator
(x 12)
ST20 CPU accessible
registers
Figure 3.1 DSP module block diagram
The main stages of processing are as follows:
Data sampling
This stage removes any meta-stability caused by the asynchronous input data coming from an
analogue source (the radio receiver). The data at this point consists of a carrier of nominally
4.092 MHz with a bandwidth of approximately ±1 MHz.
This stage is common to all 12 channels.
Frequency conversion (A)
The first frequency converter mixes the sampled IF data with the (nominal) 4.092 MHz signal. This
is done twice with a quarter cycle offset to produce I and Q (In-phase and Quadrature) versions of
the data at nominal zero centre frequency (this can actually be up to ±132 KHz due to errors such
11/116
ST20-GP1
as doppler shift, crystal accuracy, etc.). The sum frequency (~8 MHz) is removed by low-pass
filtering in the correlator.
This stage is common to all 12 channels.
Correlation against pseudo-random sequence
The GPS data is transmitted as a spread-spectrum signal (with a bandwidth of about 2 MHz). In
order to recover the data it is necessary to correlate against the same Pseudo-Random Noise
(PRN) signal that was used to transmit the data. The output of the correlator accumulator is
sampled at 264 KHz. The PRN sequences come from the PRN generator.
There is a correlator for the I and Q signals for each of the 12 channels. The output signal is now
narrowband.
Frequency conversion (B)
The second stage of frequency conversion mixes the data with the local oscillator signal generated
by the Numerically Controlled Oscillator (NCO). This signal is locked, under software control, to the
Space Vehicle (SV) frequency and phase to remove the errors and take the frequency and
bandwidth of the data down to 0 and ±50 Hz respectively. Filtering to 500 Hz is achieved in
hardware, to 50 Hz in software.
This stage is shared by time division multiplexing between all 12 channels. This is loss-free as the
stage supports 12 channels x 264 KHz, approximately 3 MHz, well within its 16 MHz clock rate.
Result integration
The final stage sums the I and Q values for each channel over a user defined period. In normal
operation, the sampling period is slightly less than the 1ms length of the PRN sequence. This
ensures that no data is lost, although it may mean that some data samples are seen twice — this is
handled (mainly) in software.
The sampling period can also be programmed to be much shorter (i.e. a higher cut-off frequency
for the filter) when the system is trying to find new satellites (‘acquisition mode’).
There are two further stages of buffering for the accumulated 16-bit I and Q values for each
1
channel. These allow for the slightly different time domains involved .
The results after hardware processing of the signal, using the parameters set in the DSP registers,
refer to Section 3.1, are delivered to the CPU via a DMA engine in packet format. The CPU should
perform an in (input) instruction on the appropriate channel (see address map, Figure 7.1 on
page 47) in order to read a packet.
The format of the 62-byte packets is given in Figure 3.2. These represent a two byte header,
followed by the 16-bit I-values for 12 channels, then the 16-bit Q-values for 12 channels, then the 8-
bit timestamp values for the 12 channels. The I and Q values are sent least significant byte first.
The 2 byte header contains: a ‘sync’ byte with the value #1B, and a ‘sample rate’ byte which
contains the two SampleRate bits from the DSPControl register, see Table 3.1.
Packets are delivered at the rate selected by the DSPControl register, even if new data is not
available. In this case, the data value for the field is set to #8000. This guarantees that synchronism
1. Data sampled in SV time, data transmitted to the CPU at fixed intervals.
12/116
ST20-GP1
is maintained between the satellite one-millisecond epochs and the receiver, despite time-of-
reception variations due to the varying path length from the satellite.
62 byte packet every 840/970/31/62 µs
12 x 16-bit
I values
12 x 16-bit
Q values
12 x 8-bit
time values
16-bit
Absent 16-bit values padded with #8000
header
sample
rate
sync
Tracking mode
Acquisition mode
T[7:6] = 10
T[5:0] = time[5:0]
First packet (in SV ms)
T[7:6] = 10
T[5:0] = time[5:0]
Remaining packets
T[7:6] = 00
T[5:0] = sequence number
(sequence numbers are 2 to
16 or 32)
Figure 3.2 DSP packet format
3.1 DSP module registers
The GPS hardware channels of the ST20-GP1 are controlled by three sets of registers:
1 DSPControl register
2 PRNcode0-11 and PRNphase0-11 registers
3 NCOfrequency0-11 and NCOphase0-11 registers
The base addresses for the DSP registers are given in the Memory Map chapter.
DSPControl register
The DSPControl register determines whether the PRN generators are on (normal use) or disabled
(for built-in-self-test of a system), whether the system is in tracking mode (840/970 µs output rate)
or initial acquisition mode (31/62 µs), and selects which of the two rates for each mode. It also
determines whether the accumulated carrier phase in the NCO are reset to zero automatically or
continue from their existing value. The bit allocations are given in Table 3.1.
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ST20-GP1
DSPControl
DSP base address + #140
Function
Write only
Bit
Bit field
1:0
SampleRate
These bits control the sampling rate (the rate at which data is sent to the DMA
controller). The encoding of these bits is as follows:
No. of samples
accumulated
SampleRate[1:0]
Transfer period
Mode
00
01
10
11
840 µs
970 µs
31 µs
256
256
8
Tracking
Acquisition
62 µs
16
2
3
NCOResetEnable
PRNDisable
When set to 1, the accumulated NCO phase for a channel is reset when the corre-
sponding PRN code register is written.
When set to 1, all PRN generators are disabled.
Table 3.1 DSPControl register format
PRNcode0-11 registers
The PRNcode0-11 registers choose the code for the particular satellite, and writing these causes a
reset to the accumulated carrier phase in the NCO for the corresponding channel, if enabled by the
DSPControl register.
PRNcode0-11
DSP base address + #00 to #2C
Write only
Bit
Bit field
PRNcode
Function
6:0
Satellite code as a 7-bit value.
Table 3.2 PRNcode0-11 register format
The bit-fields for selecting particular GPS satellites are given in Table 3.3.
a
Taps selected from G2 shift register
PRNcode0-11
register value
Satellite ID
by bits 6 to 4
by bits 3 to 0
1
2
#62
#73
#04
#15
#11
#22
#01
#12
#23
#32
#43
#65
#76
#07
#18
6
7
2
3
4
5
1
2
1
2
3
2
3
5
6
7
8
3
8
4
9
5
9
6
10
8
7
8
9
9
10
3
10
11
12
13
14
15
4
6
7
8
9
Table 3.3 PRNcode0-11 register value
14/116
ST20-GP1
a
Taps selected from G2 shift register
PRNcode0-11
register value
Satellite ID
by bits 6 to 4
by bits 3 to 0
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
-
#29
#41
#52
#63
#74
#05
#16
#31
#64
#75
#06
#17
#28
#61
#72
#03
#14
#25
#24
#71
#02
#24
#20
10
4
9
1
2
3
4
5
6
1
4
5
6
7
8
1
2
3
4
5
4
1
2
4
0
5
6
7
8
9
3
6
7
8
9
10
6
7
8
9
10
10
7
-
-
-
8
-
10
10
b
WAAS
Table 3.3 PRNcode0-11 register value
a. Refer to the US DoD document ICD-GPS-200.
b. It is the responsibility of the software to ensure that when this value is selected, a suitable value has
been written into the PRNinitialVal0-1 register. If this channel is later used for a standard GPS sat-
ellite, the PRNinitialVal0-1 must be set to all ones (#3FF).
For channels 0 and 1, RTCA-SC159 satellite codes can also be selected. This is achieved by
setting the PRNcode0-11 register appropriately and also writing the initial value for the satellite to
the PRNinitialVal0-1 register, see Table 3.8. If uninitialized by the software, the PRNinitialVal
register defaults to 11 1111 1111 (#3FF) as required for GPS satellites.
The PRNcode0-11 and PRNinitialVal0-1 registers are normally written only when the satellite is
first chosen.
PRNphase0-11 registers
The PRN0-11phase registers determine the relative delay between the receiver master clock, and
the start of the one millisecond repetitive code sequence. The code sequence starts when the
receiver clock counter (invisible to the software except through message timestamps) reaches the
value written to the PRNphase0-11 register. The PRNphase0-11 register must only be written
once per satellite milliseconds-epoch, which varies from the receiver epoch dynamically due to
satellite motion. Synchronism with the software is achieved by reading the register, when a write
enable flag is returned. If not enabled, the write operation is abandoned by the software.
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The 19-bit value comprises three fields. The 3 least significant bits represent the fractional-delay in
eighths of a code-chip. The middle 10 bits represent the integer delay in code-chips, 0-1022, with
the value 1023 illegal. The upper 6 most significant bits represent the delay in integer milliseconds.
PRNphase0-11
DSP base address + #40 to #6C
Function
Write only
Bit
Bit field
FractionalDelay
2:0
Fractional delay in eighths of a code-chip.
12:3
18:13
IntegerDelay
Delay
Integer delay in code-chips. Value 0-1022. Note, the value 1023 is illegal.
Delay in integer milliseconds.
Table 3.4 PRNphase0-11 register format
Note also that the eighth-chip resolution of the code generator is not sufficient for positioning. At
125 ns it represents approximately 40 m of range, over 100 m of position. The software must
maintain the range measurements around the 1 ns resolution level in a 32-bit field, and send an
appropriate 19-bit sub-field to the register. Note, care must be taken when calculating this field from
a computed delay, or vice versa, to allow for the missing value 1023. The overall register bit-field
cannot be used mathematically as a single binary number.
PRNphase0-11WrEn registers
The PRNphase0-11WrEn flags are active low flags that record when the PRNphase0-11 register
can be updated. The PRNphaseWrEn flag for a channel is set high when the corresponding
PRNphase register is written. The flag is reset again when the value written is loaded into the PRN
generator. Note, the PRNphase0-11 register should only be updated when the PRNphase0-
11WrEn register has been cleared by the hardware.
PRNphase0-11WrEn
DSP base address + #40 to #6C
Function
Read only
Bit
Bit field
PRNphaseWrEn
0
Set when the corresponding PRNphase0-11 register is set.
Table 3.5 PRNphase0-11WrEn register format
NCOfrequency0-11 registers
The NCOfrequency0-11 registers hold a signed 18-bit value that is added repetitively, ignoring
overflows, to the accumulated NCO phase from which the NCO sine and cosine waveforms are
generated. The addition is performed at a 264 KHz rate (16.368MHz/62). The accumulated NCO
phase is not accessible to the software, but can be cleared when initialising the channel if enabled
by the DSPControl register.
18
Each unit value in the NCOfrequency0-11 register represents 264KHz/(2 ), i.e.
1.007080078125 Hz.
If the extreme values are written, #1FFFF and #20000, the sine wave generated will be at
approximately +132 KHz, and precisely -132 KHz respectively.
NCOfrequency0-11
DSP base address + #80 to #AC
Write only
Bit
Bit field
Function
17:0
NCOfrequency
NCO frequency as a signed 18-bit value.
Table 3.6 NCOfrequency0-11 register format
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NCOphase0-11 registers
The NCOphase0-11 registers contents are added to the accumulated phase to correct the carrier
for the final 1 Hz that cannot be resolved by the NCO frequency. This addition is not cumulative,
and the value must be updated regularly by the software as a result of carrier phase errors
measured on the satellite signal. The register holds a signed 7-bit field representing +/-180
degrees total in steps of 2.8125 degrees (360/128).
NCOphase0-11
DSP base address + #C4 to #EC
Function
Write only
Bit
Bit field
NCOphase
6:0
NCO phase as a signed 7-bit value representing +/-180 degrees total in steps of
2.8125 degrees (360/128).
Table 3.7 NCOphase0-11 register format
PRNinitialVal0-1 registers
The initial value for the two RTCA-SC159 capable satellites channels should be written to the
PRNinitialVal0-1 registers. The value can be found in the RTCA-SC159 Specification.
Note: The value written to the register is the Initial Value defined by RTCA-SC159 for the PRN
required. The conversion from ‘big-endian’ as used in the specification to ‘little-endian’ as
conventionally used in ST20 architectures has been implemented in the hardware.
If uninitialized by the software, this register defaults to 11 1111 1111 (#3FF) as required for GPS
satellites.
PRNinitialVal0-1
DSP base address + #100, #104
Write only
Bit
Bit field
Function
9:0
InitialValue
Initial value of the RTCA-SC159 satellite channel.
Table 3.8 PRNinitialVal0-1 register format
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4 Central processing unit
The Central Processing Unit (CPU) is the ST20 32-bit processor core. It contains instruction
processing logic, instruction and data pointers, and an operand register. It can directly access the
high speed on-chip memory, which can store data or programs. Where larger amounts of memory
are required, the processor can access memory via the External Memory Interface (EMI).
The processor provides high performance:
•
•
•
•
•
Fast integer multiply — 3 cycle multiply
Fast bit shift — single cycle barrel shifter
Byte and part-word handling
Scheduling and interrupt support
64-bit integer arithmetic support
The scheduler provides a single level of pre-emption. In addition, multi-level pre-emption is
provided by the interrupt subsystem, see Chapter 5 for details. Additionally, there is a per-priority
trap handler to improve the support for arithmetic errors and illegal instructions, refer to section 4.6.
4.1 Registers
The CPU contains six registers which are used in the execution of a sequential integer process.
The six registers are:
•
•
•
•
The workspace pointer (Wptr) which points to an area of store where local data is kept.
The instruction pointer (IptrReg) which points to the next instruction to be executed.
The status register (StatusReg).
The Areg, Breg and Creg registers which form an evaluation stack.
The Areg, Breg and Creg registers are the sources and destinations for most arithmetic and
logical operations. Loading a value into the stack pushes Breg into Creg, and Areg into Breg,
before loading Areg. Storing a value from Areg, pops Breg into Areg and Creg into Breg. Creg is
left undefined.
Registers
Local data
Program
Areg
Breg
Creg
Wptr
IptrReg
Figure 4.1 Registers used in sequential integer processes
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Expressions are evaluated on the evaluation stack, and instructions refer to the stack implicitly. For
example, the add instruction adds the top two values in the stack and places the result on the top of
the stack. The use of a stack removes the need for instructions to explicitly specify the location of
their operands. No hardware mechanism is provided to detect that more than three values have
been loaded onto the stack; it is easy for the compiler to ensure that this never happens.
Note that a location in memory can be accessed relative to the workspace pointer, enabling the
workspace to be of any size.
The use of shadow registers provides fast, simple and clean context switching.
4.2 Processes and concurrency
The following section describes ‘default’ behavior of the CPU and it should be noted that the user
can alter this behavior, for example, by disabling timeslicing, installing a user scheduler, etc.
A process starts, performs a number of actions, and then either stops without completing or
terminates complete. Typically, a process is a sequence of instructions. The CPU can run several
processes in parallel (concurrently). Processes may be assigned either high or low priority, and
there may be any number of each.
The processor has a microcoded scheduler which enables any number of concurrent processes to
be executed together, sharing the processor time. This removes the need for a software kernel,
although kernels can still be written if desired.
At any time, a process may be
active
- being executed
- interrupted by a higher priority process
- on a list waiting to be executed
inactive - waiting to input
- waiting to output
- waiting until a specified time
The scheduler operates in such a way that inactive processes do not consume any processor time.
Each active high priority process executes until it becomes inactive. The scheduler allocates a
portion of the processor’s time to each active low priority process in turn (see Section 4.3). Active
processes waiting to be executed are held in two linked lists of process workspaces, one of high
priority processes and one of low priority processes. Each list is implemented using two registers,
one of which points to the first process in the list, the other to the last. In the linked process list
shown in Figure 4.2, process S is executing and P, Q and R are active, awaiting execution. Only the
low priority process queue registers are shown; the high priority process ones behave in a similar
manner.
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Local Data
pw.Iptr
Registers
FptrReg1
BptrReg1
Program
P
Q
R
S
pw.Link
pw.Iptr
pw.Link
Areg
pw.Iptr
Breg
Creg
Wptr
IptrReg
Figure 4.2 Linked process list
Function
High priority
Low priority
Pointer to front of active process list
Pointer to back of active process list
FptrReg0
BptrReg0
FptrReg1
BptrReg1
Table 4.1 Priority queue control registers
Each process runs until it has completed its action or is descheduled. In order for several
processes to operate in parallel, a low priority process is only permitted to execute for a maximum
of two timeslice periods. After this, the machine deschedules the current process at the next
timeslicing point, adds it to the end of the low priority scheduling list and instead executes the next
active process. The timeslice period is 1ms.
There are only certain instructions at which a process may be descheduled. These are known as
descheduling points. A process may only be timesliced at certain descheduling points. These are
known as timeslicing points and are defined in such a way that the operand stack is always empty.
This removes the need for saving the operand stack when timeslicing. As a result, an expression
evaluation can be guaranteed to execute without the process being timesliced part way through.
Whenever a process is unable to proceed, its instruction pointer is saved in the process workspace
and the next process taken from the list.
The processor core provides a number of special instructions to support the process model,
including startp (start process) and endp (end process). When a main process executes a parallel
construct, startp is used to create the necessary additional concurrent processes. A startp
instruction creates a new process by adding a new workspace to the end of the scheduling list,
enabling the new concurrent process to be executed together with the ones already being
executed. When a process is made active it is always added to the end of the list, and thus cannot
pre-empt processes already on the same list.
The correct termination of a parallel construct is assured by use of the endp instruction. This uses
a data structure that includes a counter of the parallel construct components which have still to
terminate. The counter is initialized to the number of components before the processes are started.
Each component ends with an endp instruction which decrements and tests the counter. For all but
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the last component, the counter is non zero and the component is descheduled. For the last
component, the counter is zero and the main process continues.
4.3 Priority
The following section describes ‘default’ behavior of the CPU and it should be noted that the user
can alter this behavior, for example, by disabling timeslicing and priority interrupts.
The processor can execute processes at one of two priority levels, one level for urgent (high
priority) processes, one for less urgent (low priority) processes. A high priority process will always
execute in preference to a low priority process if both are able to do so.
High priority processes are expected to execute for a short time. If one or more high priority
processes are active, then the first on the queue is selected and executes until it has to wait for a
communication, a timer input, or until it completes processing.
If no process at high priority is active, but one or more processes at low priority are active, then one
is selected. Low priority processes are periodically timesliced to provide an even distribution of
processor time between computationally intensive tasks.
If there are n low priority processes, then the maximum latency from the time at which a low priority
process becomes active to the time when it starts processing is the order of 2n timeslice periods. It
is then able to execute for between one and two timeslice periods, less any time taken by high
priority processes. This assumes that no process monopolizes the CPU’s time; i.e. it has frequent
timeslicing points.
The specific condition for a high priority process to start execution is that the CPU is idle or running
at low priority and the high priority queue is non-empty.
If a high priority process becomes able to run whilst a low priority process is executing, the low
priority process is temporarily stopped and the high priority process is executed. The state of the
low priority process is saved into ‘shadow’ registers and the high priority process is executed.
When no further high priority processes are able to run, the state of the interrupted low priority
process is re-loaded from the shadow registers and the interrupted low priority process continues
executing. Instructions are provided on the processor core to allow a high priority process to store
the shadow registers to memory and to load them from memory. Instructions are also provided to
allow a process to exchange an alternative process queue for either priority process queue (see
Table 6.21 on page 43). These instructions allow extensions to be made to the scheduler for
custom runtime kernels.
A low priority process may be interrupted after it has completed execution of any instruction. In
addition, to minimize the time taken for an interrupting high priority process to start executing, the
potentially time consuming instructions are interruptible. Also some instructions are abortable and
are restarted when the process next becomes active (refer to the Instruction Set chapter).
4.4 Process communications
Communication between processes takes place over channels, and is implemented in hardware.
Communication is point-to-point, synchronized and unbuffered. As a result, a channel needs no
process queue, no message queue and no message buffer.
A channel between two processes executing on the same CPU is implemented by a single word in
memory; a channel between processes executing on different processors is implemented by point-
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to-point links. The processor provides a number of operations to support message passing, the
most important being in (input message) and out (output message).
The in and out instructions use the address of the channel to determine whether the channel is
internal or external. This means that the same instruction sequence can be used for both hard and
soft channels, allowing a process to be written and compiled without knowledge of where its
channels are implemented.
Communication takes place when both the inputting and outputting processes are ready.
Consequently, the process which first becomes ready must wait until the second one is also ready.
The inputting and outputting processes only become active when the communication has
completed.
A process performs an input or output by loading the evaluation stack with, a pointer to a message,
the address of a channel, and a count of the number of bytes to be transferred, and then executing
an in or out instruction.
4.5 Timers
There are two 32-bit hardware timer clocks which ‘tick’ periodically. These are independent of any
on-chip peripheral real time clock. The timers provide accurate process timing, allowing processes
to deschedule themselves until a specific time.
One timer is accessible only to high priority processes and is incremented every microsecond,
cycling completely in approximately 4295 seconds. The other is accessible only to low priority
processes and is incremented every 64 microseconds, giving 15625 ticks in one second. It has a
full period of approximately 76 hours. All times are approximate due to the clock rate.
Register
Function
ClockReg0
ClockReg1
TnextReg0
TnextReg1
TptrReg0
TptrReg1
Current value of high priority (level 0) process clock
Current value of low priority (level 1) process clock
Indicates time of earliest event on high priority (level 0) timer queue
Indicates time of earliest event on low priority (level 1) timer queue
High priority timer queue
Low priority timer queue
Table 4.2 Timer registers
The current value of the processor clock can be read by executing a ldtimer (load timer) instruction.
A process can arrange to perform a tin (timer input), in which case it will become ready to execute
after a specified time has been reached. The tin instruction requires a time to be specified. If this
time is in the ‘past’ then the instruction has no effect. If the time is in the ‘future’ then the process is
descheduled. When the specified time is reached the process becomes active. In addition, the
ldclock (load clock), stclock (store clock) instructions allow total control over the clock value and the
clockenb (clock enable), clockdis (clock disable) instructions allow each clock to be individually
stopped and re-started.
Figure 4.3 shows two processes waiting on the timer queue, one waiting for time 21, the other for
time 31.
Note, these timers stop counting when power-down mode (see Section 10.2 on page 61) is
invoked.
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Workspaces
Program
ClockReg0
TnextReg0
TptrReg0
5
comparator
21
Alarm
21
Empty
31
Figure 4.3 Timer registers
4.6 Traps and exceptions
A software error, such as arithmetic overflow or array bounds violation, can cause an error flag to
be set in the CPU. The flag is directly connected to the ErrorOut pin. Both the flag and the pin can
be ignored, or the CPU stopped. Stopping the CPU on an error means that the error cannot cause
further corruption. As well as containing the error in this way it is possible to determine the state of
the CPU and its memory at the time the error occurred. This is particularly useful for postmortem
debugging where the debugger can be used to examine the state and history of the processor
leading up to and causing the error condition.
In addition, if a trap handler process is installed, a variety of traps/exceptions can be trapped and
handled by software. A user supplied trap handler routine can be provided for each high/low
process priority level. The handler is started when a trap occurs and is given the reason for the
trap. The trap handler is not re-entrant and must not cause a trap itself within the same group. All
traps are individually maskable.
4.6.1 Trap groups
The trap mechanism is arranged on a per priority basis. For each priority there is a handler for each
group of traps, as shown in Figure 4.4.
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Low priority traps
High priority traps
Scheduler
trap handler
Scheduler
trap handler
CPU Error
trap handler
CPU Error
trap handler
Breakpoint
trap handler
System operations
trap handler
Breakpoint
trap handler
System operations
trap handler
Figure 4.4 Trap arrangement
There are four groups of traps, as detailed below.
•
Breakpoint
This group consists of the Breakpoint trap. The breakpoint instruction (j0) calls the break-
point routine via the trap mechanism.
•
Errors
The traps in this group are IntegerError and Overflow. Overflow represents arithmetic over-
flow, such as arithmetic results which do not fit in the result word. IntegerError represents
errors caused when data is erroneous, for example when a range checking instruction finds
that data is out of range.
•
•
System operations
This group consists of the LoadTrap, StoreTrap and IllegalOpcode traps. The IllegalOpcode
trap is signalled when an attempt is made to execute an illegal instruction. The LoadTrap
and StoreTrap traps allow a kernel to intercept attempts by a monitored process to change
or examine trap handlers or trapped process information. It enables a user program to sig-
nal to a kernel that it wishes to install a new trap handler.
Scheduler
The scheduler trap group consists of the ExternalChannel, InternalChannel, Timer, TimeS-
lice, Run, Signal, ProcessInterrupt and QueueEmpty traps. The ProcessInterrupt trap sig-
nals that the machine has performed a priority interrupt from low to high. The QueueEmpty
trap indicates that there is no further executable work to perform. The other traps in this
group indicate that the hardware scheduler wants to schedule a process on a process
queue, with the different traps enabling the different sources of this to be monitored.
The scheduler traps enable a software scheduler kernel to use the hardware scheduler to
implement a multi-priority software scheduler.
Note that scheduler traps are different from other traps as they are caused by the micro-
scheduler rather than by an executing process.
Note, when the scheduler trap is caused by a process that is ready to be scheduled, the
Wptr of that process is stored in the workspace of the scheduler trap handler, at address 0.
The trap handler can access this using a ldl 0 instruction.
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Trap groups encoding is shown in Table 4.4 below. These codes are used to identify trap groups to
various instructions.
Trap group
Breakpoint
Code
0
1
2
3
CPU Errors
System operations
Scheduler
Table 4.3 Trap group codes
In addition to the trap groups mentioned above, the CauseError flag in the Status register is used
to signal when a trap condition has been activated by the causeerror instruction. It can be used to
indicate when trap conditions have occurred due to the user setting them, rather than by the
system.
4.6.2 Events that can cause traps
Table 4.4 summarizes the events that can cause traps and gives the encoding of bits in the trap
Status and Enable words.
Trap cause
Breakpoint
IntegerError
Status/Enable
codes
Trap
group
Comments
0
0
When a process executes the breakpoint instruction (j0) then it traps
to its trap handler.
1
1
Integer error other than integer overflow – e.g. explicitly checked or
explicitly set error.
Overflow
2
3
1
2
Integer overflow or integer division by zero.
IllegalOpcode
Attempt to execute an illegal instruction. This is signalled when opr
(operate) is executed with an invalid operand.
LoadTrap
StoreTrap
4
5
2
2
When the trap descriptor is read with the ldtraph (load trap handler)
instruction or when the trapped process status is read with the
ldtrapped (load trapped) instruction.
When the trap descriptor is written with the sttraph (store trap handler)
instruction or when the trapped process status is written with the
sttrapped (store trapped) instruction.
InternalChannel
ExternalChannel
Timer
6
3
3
Scheduler trap from internal channel.
7
Scheduler trap from external channel.
8
3
Scheduler trap from timer alarm.
Timeslice
9
3
Scheduler trap from timeslice.
Run
10
3
Scheduler trap from runp (run process) or startp (start process).
Scheduler trap from signal.
Signal
11
3
ProcessInterrupt
QueueEmpty
CauseError
12
13
3
Start executing a process at a new priority level.
Caused by no process active at a priority level.
Signals that the causeerror instruction set the trap flag.
3
15 (Status only)
Any,
encoded
0-3
Table 4.4 Trap causes and Status/Enable codes
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4.6.3 Trap handlers
For each trap handler there is a trap handler structure and a trapped process structure. Both the
trap handler structure and the trapped process structure are in memory and can be accessed via
instructions, see Section 4.6.4.
The trap handler structure specifies what should happen when a trap condition is present, see
Table 4.6.
Comments
Iptr
Iptr of trap handler process.
Base + 3
Base + 2
Base + 1
Wptr
Wptr of trap handler process.
Status
Enables
Contains the Status register that the trap handler starts with.
Contains a word which encodes the trap enable and global interrupt masks which will be Base + 0
ANDed with the existing masks to allow the trap handler to disable various events while it
runs.
Table 4.5 Trap handler structure
The trapped process structure saves some of the state of the process that was running when the
trap was taken, see Table 4.7.
Comments
Iptr
Points to the instruction after the one that caused the trap condition.
Wptr of the process that was running when the trap was taken.
The relevant trap bit is set, see Table 4.5 for trap codes.
Interrupt enables.
Base + 3
Base + 2
Base + 1
Base + 0
Wptr
Status
Enables
Table 4.6 Trapped process structure
In addition, for each priority, there is an Enables register and a Status register. The Enables
register contains flags to enable each cause of trap. The Status register contains flags to indicate
which trap conditions have been detected. The Enables and Status register bit encodings are
given in Table 4.4.
A trap will be taken at an interruptible point if a trap is set and the corresponding trap enable bit is
set in the Enables register. If the trap is not enabled then nothing is done with the trap condition. If
the trap is enabled then the corresponding bit is set in the Status register to indicate the trap
condition has occurred.
When a process takes a trap the processor saves the existing Iptr, Wptr, Status and Enables in
the trapped process structure. It then loads Iptr, Wptr and Status from the equivalent trap handler
structure and ANDs the value in Enables with the value in the structure. This allows the user to
disable various events while in the handler, in particular a trap handler must disable all the traps of
its trap group to avoid the possibility of a handler trapping to itself.
The trap handler then executes. The values in the trapped process structure can be examined
using the ldtrapped instruction (see Section 4.6.4). When the trap handler has completed its
operation it returns to the trapped process via the tret (trap return) instruction. This reloads the
values saved in the trapped process structure and clears the trap flag in Status.
Note that when a trap handler is started, Areg, Breg and Creg are not saved. The trap handler
must save the Areg, Breg, Creg registers using stl (store local).
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4.6.4 Trap instructions
Trap handlers and trapped processes can be set up and examined via the ldtraph, sttraph,
ldtrapped and sttrapped instructions. Table 4.8 describes the instructions that may be used when
dealing with traps.
Instruction Meaning
Use
ldtraph
load trap handler
load the trap handler from memory to the trap handler descriptor
store an existing trap handler descriptor to memory
load replacement trapped process status from memory
store trapped process status to memory
enable traps
sttraph
store trap handler
load trapped
store trapped
trap enable
ldtrapped
sttrapped
trapenb
trapdis
trap disable
trap return
disable traps
tret
used to return from a trap handler
program can simulate the occurrence of an error
causeerror
cause error
Table 4.7 Instructions which may be used when dealing with traps
The first four instructions transfer data to/from the trap handler structures or trapped process
structures from/to an area in memory. In these instructions Areg contains the trap group code (see
Table 4.4) and Breg points to the 4 word area of memory used as the source or destination of the
transfer. In addition Creg contains the priority of the handler to be installed/examined in the case of
ldtraph or sttraph. ldtrapped and sttrapped apply only to the current priority.
If the LoadTrap trap is enabled then ldtraph and ldtrapped do not perform the transfer but set the
LoadTrap trap flag. If the StoreTrap trap is enabled then sttraph and sttrapped do not perform the
transfer but set the StoreTrap trap flag.
The trap enable masks are encoded by an array of bits (see Table 4.5) which are set to indicate
which traps are enabled. This array of bits is stored in the lower half-word of the Enables register.
There is an Enables register for each priority. Traps are enabled or disabled by loading a mask into
Areg with bits set to indicate which traps are to be affected and the priority to affect in Breg.
Executing trapenb ORs the mask supplied in Areg with the trap enables mask in the Enables
register for the priority in Breg. Executing trapdis negates the mask supplied in Areg and ANDs it
with the trap enables mask in the Enables register for the priority in Breg. Both instructions return
the previous value of the trap enables mask in Areg.
4.6.5 Restrictions on trap handlers
There are various restrictions that must be placed on trap handlers to ensure that they work
correctly.
1 Trap handlers must not deschedule or timeslice. Trap handlers alter the Enables masks,
therefore they must not allow other processes to execute until they have completed.
2 Trap handlers must have their Enable masks set to mask all traps in their trap group to
avoid the possibility of a trap handler trapping to itself.
3 Trap handlers must terminate via the tret (trap return) instruction. The only exception to this
is that a scheduler kernel may use restart to return to a previously shadowed process.
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5 Interrupt controller
The ST20-GP1 supports external interrupts, enabling an on-chip subsystem or external interrupt
pin to interrupt the currently running process in order to run an interrupt handling process.
The ST20-GP1 interrupt subsystem supports five prioritized interrupts. This allows nested pre-
emptive interrupts for real-time system design. Three interrupts are connected to on-chip
peripherals (2 for the UARTs, 1 for the programmable IO) and two are available as external
interrupt pins.
All interrupts are at a higher priority than the high priority process queue, see Figure 5.1. Each
interrupt level has a higher priority than the previous (interrupt 0 is lowest priority) and each level
supports only one software handler process.Note that interrupt handlers must not prevent the GPS
DSP data traffic from being handled. During continuous operation this has 1 ms latency and is not
a problem, but during initial acquisition it has a 32 µs rate and thus all interrupts must be disabled
except if used to stop GPS operation.
Interrupt 4
Interrupt1 pin
Interrupt 3
Interrupt0 pin
Interrupt 2
UART1
Interrupt 1
UART0
Increasing
pre-emption
Interrupt 0
Programmable IO
High priority
process
Low priority
process
Figure 5.1 Interrupt priority
Interrupts on the ST20-GP1 are implemented via an on-chip interrupt controller peripheral. An
interrupt can be signalled to the controller by one of the following:
•
•
•
a signal on an external Interrupt pin
a signal from an internal peripheral or subsystem
software asserting an interrupt in a bit mask
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5.1 Interrupt vector table
The interrupt controller contains a table of pointers to interrupt handlers. Each interrupt handler is
represented by its workspace pointer (Wptr). The table contains a workspace pointer for each level
of interrupt.
The Wptr gives access to the code, data and interrupt save space of the interrupt handler. The
position of the Wptr in the interrupt table implies the priority of the interrupt.
Run-time library support is provided for setting and programming the vector table.
5.2 Interrupt handlers
At any interruptible point in its execution the CPU can receive an interrupt request from the
interrupt controller. The CPU immediately acknowledges the request.
In response to receiving an interrupt the CPU performs a procedure call to the process in the
vector table. The state of the interrupted process is stored in the workspace of the interrupt handler
as shown in Figure 5.2. Each interrupt level has its own workspace.
Before interrupt
Interrupting high priority
process
Interrupting low priority
process or CPU idle
Wptr
Wptr
Wptr
Handler Iptr
Handler Iptr
Handler Status
Creg
Handler Iptr
Handler Status
Handler Status
Breg
Areg
Iptr
Wptr
Status
Null Status
Figure 5.2 State of interrupted process
The interrupt routine is initialized with space below Wptr. The Iptr and Status word for the routine
are stored there permanently. This should be programmed before the Wptr is written into the vector
table. The behavior of the interrupt differs depending on the priority of the CPU when the interrupt
occurs.
When an interrupt occurs when the CPU was running at high priority, the CPU saves the current
process state (Areg, Breg, Creg, Wptr, Iptr and Status) into the workspace of the interrupt
handler. The value HandlerWptr, which is stored in the interrupt controller, points to the top of this
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workspace. The values of Iptr and Status to be used by the interrupt handler are loaded from this
workspace and starts executing the handler. The value of Wptr is then set to the bottom of this
save area.
When an interrupt occurs when the CPU was idle or running at low priority, the Status is saved.
This indicates that no valid process is running (Null Status). The interrupted processes (low priority
process) state is stored in shadow registers. This state can be accessed via the ldshadow (load
shadow registers) and stshadow (store shadow registers) instructions. The interrupt handler is then
run at high priority.
When the interrupt routine has completed it must adjust Wptr to the value at the start of the
handler code and then execute the iret (interrupt return) instruction. This restores the interrupted
state from the interrupt handler structure and signals to the interrupt controller that the interrupt has
completed. The processor will then continue from where it was before being interrupted.
5.3 Interrupt latency
The interrupt latency is dependent on the data being accessed and the position of the interrupt
handler and the interrupted process. This allows systems to be designed with the best trade-off use
of fast internal memory and interrupt latency.
5.4 Pre-emption and interrupt priority
Each interrupt channel has an implied priority fixed by its place in the interrupt vector table. All
interrupts will cause scheduled processes of any priority to be suspended and the interrupt handler
started. Once an interrupt has been sent from the controller to the CPU the controller keeps a
record of the current executing interrupt priority. This is only cleared when the interrupt handler
executes a return from interrupt (iret) instruction. Interrupts of a lower priority arriving will be
blocked by the interrupt controller until the interrupt priority has descended to such a level that the
routine will execute. An interrupt of a higher priority than the currently executing handler will be
passed to the CPU and cause the current handler to be suspended until the higher priority interrupt
is serviced.
In this way interrupts can be nested and a higher priority interrupt will always pre-empt a lower
priority one. Deep nesting and placing frequent interrupts at high priority can result in a system
where low priority interrupts are never serviced or the controller and CPU time are consumed in
nesting interrupt priorities and not executing the interrupt handlers.
5.5 Restrictions on interrupt handlers
There are various restrictions that must be placed on interrupt handlers to ensure that they interact
correctly with the rest of the process model implemented in the CPU.
1 Interrupt handlers must not deschedule.
2 Interrupt handlers must not execute communication instructions. However they may com-
municate with other processes through shared variables using the semaphore signal to
synchronize.
3 Interrupt handlers must not perform block move instructions.
4 Interrupt handlers must not cause program traps. However they may be trapped by a
scheduler trap.
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5.6 Interrupt configuration registers
The interrupt controller is allocated a 4k block of memory in the internal peripheral address space.
Information on interrupts is stored in registers as detailed in the following section. The registers can
be examined and set by the devlw (device load word) and devsw (device store word) instructions.
Note, they can not be accessed using memory instructions.
HandlerWptr register
The HandlerWptr registers (1 per interrupt) contain a pointer to the workspace of the interrupt
handler.
Note, before the interrupt is enabled, by writing a 1 in the Mask register, the user (or toolset) must
ensure that there is a valid Wptr in the register.
HandlerWptr0-4
Interrupt controller base address + #00 to #10
Function
Read/Write
Bit
Bit field
31:2
1:0
HandlerWptr
Pointer to the workspace of the interrupt handler.
RESERVED. Write 0.
Table 5.1 HandlerWptr register format — one register per interrupt
TriggerMode register
Each interrupt channel can be programmed to trigger on rising/falling edges or high/low levels on
the external Interrupt.
TriggerMode0-4
Interrupt controller base address + #40 to #50
Function
Read/Write
Bit
Bit field
Trigger
2:0
Control the triggering condition of the Interrupt, as follows:
Trigger2:0 Interrupt triggers on
000
No trigger mode
001
010
011
100
101
High level - triggered while input high
Low level - triggered while input low
Rising edge - low to high transition
Falling edge - high to low transition
Any edge - triggered on rising and falling edges
110
111
No trigger mode
No trigger mode
Table 5.2 TriggerMode register format — one register per interrupt
Note, level triggering is different to edge triggering in that if the input is held at the triggering level, a
continuous stream of interrupts is generated.
Mask register
An interrupt mask register is provided in the interrupt controller to selectively enable or disable
external interrupts. This mask register also includes a global interrupt disable bit to disable all
external interrupts whatever the state of the individual interrupt mask bits.
To complement this the interrupt controller also includes an interrupt pending register which
contains a pending flag for each interrupt channel. The Mask register performs a masking function
on the Pending register to give control over what is allowed to interrupt the CPU while retaining the
ability to continually monitor external interrupts.
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On start-up, the Mask register is initialized to zero’s, thus all interrupts are disabled, both globally
and individually. When a 1 is written to the GlobalEnable bit, the individual interrupt bits are still
disabled and must also have a 1 individually written to the InterruptEnable bit to enable the
respective interrupt.
Mask
Interrupt controller base address + #C0
Function
Read/Write
Bit
0
Bit field
Interrupt0Enable
Interrupt1Enable
Interrupt2Enable
Interrupt3Enable
Interrupt4Enable
GlobalEnable
When set to 1, interrupt 0 is enabled. When 0, interrupt 0 is disabled.
When set to 1, interrupt 1 is enabled. When 0, interrupt 1 is disabled.
When set to 1, interrupt 2 is enabled. When 0, interrupt 2 is disabled.
When set to 1, interrupt 3 is enabled. When 0, interrupt 3 is disabled.
When set to 1, interrupt 4 is enabled. When 0, interrupt 4 is disabled.
1
2
3
4
16
When set to 1, the setting of the interrupt is determined by the specific InterruptEn-
able bit. When 0, all interrupts are disabled.
15:5
RESERVED. Write 0.
Table 5.3 Mask register format
The Mask register is mapped onto two additional addresses so that bits can be set or cleared
individually.
Set_Mask (address ‘interrupt base address + #C4’) allows bits to be set individually. Writing a ‘1’ in
this register sets the corresponding bit in the Mask register, a ‘0’ leaves the bit unchanged.
Clear_Mask (address ‘interrupt base address + #C8’) allows bits to be cleared individually. Writing
a ‘1’ in this register resets the corresponding bit in the Mask register, a ‘0’ leaves the bit
unchanged.
Pending register
The Pending register contains a bit per interrupt with each bit controlled by the corresponding
interrupt. A read can be used to examine the state of the interrupt controller while a write can be
used to explicitly trigger an interrupt.
A bit is set when the triggering condition for an interrupt is met. All bits are independent so that
several bits can be set in the same cycle. Once a bit is set, a further triggering condition will have
no effect. The triggering condition is independent of the Mask register.
The highest priority interrupt bit is reset once the interrupt controller has made an interrupt request
to the CPU.
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The interrupt controller receives external interrupt requests and makes an interrupt request to the
CPU when it has a pending interrupt request of higher priority than the currently executing interrupt
handler.
Pending
Interrupt controller base address + #80
Function
Read/Write
Bit
0
Bit field
PendingInt0
PendingInt1
PendingInt2
PendingInt3
PendingInt4
Interrupt 0 pending bit.
Interrupt 1 pending bit.
Interrupt 2 pending bit.
Interrupt 3 pending bit.
Interrupt 4 pending bit.
1
2
3
4
Table 5.4 Pending register format
The Pending register is mapped onto two additional addresses so that bits can be set or cleared
individually.
Set_Pending (address ‘interrupt base address + #84’) allows bits to be set individually. Writing a
‘1’ in this register sets the corresponding bit in the Pending register, a ‘0’ leaves the bit unchanged.
Clear_Pending (address ‘interrupt base address + #88’) allows bits to be cleared individually.
Writing a ‘1’ in this register resets the corresponding bit in the Pending register, a ‘0’ leaves the bit
unchanged.
Note, if the CPU wants to write or clear some bits of the Pending register, the interrupts should be
masked (by writing or clearing the Mask register) before writing or clearing the Pending register.
The interrupts can then be unmasked.
Exec register
The Exec register keeps track of the currently executing and pre-empted interrupts. A bit is set
when the CPU starts running code for that interrupt. The highest priority interrupt bit is reset once
the interrupt handler executes a return from interrupt (iret).
Exec
Interrupt controller base address + #100
Read/Write
Bit
0
Bit field
Function
Interrupt0Exec
Interrupt1Exec
Interrupt2Exec
Interrupt3Exec
Interrupt4Exec
Set to 1 when the CPU starts running code for interrupt 0.
Set to 1 when the CPU starts running code for interrupt 1.
Set to 1 when the CPU starts running code for interrupt 2.
Set to 1 when the CPU starts running code for interrupt 3.
Set to 1 when the CPU starts running code for interrupt 4.
1
2
3
4
Table 5.5 Exec register format
The Exec register is mapped onto two additional addresses so that bits can be set or cleared
individually.
Set_Exec (address ‘interrupt base address + #104’) allows bits to be set individually. Writing a ‘1’
in this register sets the corresponding bit in the Exec register, a ‘0’ leaves the bit unchanged.
Clear_Exec (address ‘interrupt base address + #108’) allows bits to be cleared individually. Writing
a ‘1’ in this register resets the corresponding bit in the Exec register, a ‘0’ leaves the bit unchanged.
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6 Instruction set
This chapter provides information on the instruction set. It contains tables listing all the instructions,
and where applicable provides details of the number of processor cycles taken by an instruction.
The instruction set has been designed for simple and efficient compilation of high-level languages.
All instructions have the same format, designed to give a compact representation of the operations
occurring most frequently in programs.
Each instruction consists of a single byte divided into two 4-bit parts. The four most significant bits
(MSB) of the byte are a function code and the four least significant bits (LSB) are a data value, as
shown in Figure 6.1.
Function
Data
7
4 3
0
Figure 6.1 Instruction format
For further information on the instruction set refer to the ST20 Instruction Set Manual (document
number 72-TRN-273-01).
6.1 Instruction cycles
Timing information is available for some instructions. However, it should be noted that many
instructions have ranges of timings which are data dependent.
Where included, timing information is based on the number of clock cycles assuming any memory
accesses are to 2 cycle internal memory and no other subsystem is using memory. Actual time will
be dependent on the speed of external memory and memory bus availability.
Note that the actual time can be increased by:
1 the instruction requiring a value on the register stack from the final memory read in the pre-
vious instruction — the current instruction will stall until the value becomes available.
2 the first memory operation in the current instruction can be delayed while a preceding
memory operation completes — any two memory operations can be in progress at any
time, any further operation will stall until the first completes.
3 memory operations in current instructions can be delayed by access by instruction fetch or
subsystems to the memory interface.
4 there can be a delay between instructions while the instruction fetch unit fetches and par-
tially decodes the next instruction — this will be the case whenever an instruction causes
the instruction flow to jump.
Note that the instruction timings given refer to ‘standard’ behavior and may be different if, for
example, traps are set by the instruction.
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6.2 Instruction characteristics
The Primary Instructions Table 6.3 gives the basic function code. Where the operand is less than
16, a single byte encodes the complete instruction. If the operand is greater than 15, one prefix
instruction (pfix) is required for each additional four bits of the operand. If the operand is negative
the first prefix instruction will be nfix. Examples of pfix and nfix coding are given in Table 6.1.
Mnemonic
Function code
Memory code
ldc
#3
#4
#43
ldc
#35
is coded as
pfix
#3
#2
#4
#23
#45
ldc
#5
ldc
#987
is coded as
pfix
#9
#8
#7
#2
#2
#4
#29
#28
#47
pfix
ldc
ldc
-31 ( ldc #FFFFFFE1)
is coded as
nfix
#1
#1
#6
#61
#41
ldc
#4
Table 6.1 Prefix coding
Any instruction which is not in the instruction set tables is an invalid instruction and is flagged
illegal, returning an error code to the trap handler, if loaded and enabled.
The Notes column of the tables indicates the descheduling and error features of an instruction as
described in Table 6.2.
Ident Feature
E
L
Instruction can set an IntegerError trap
Instruction can cause a LoadTrap trap
Instruction can cause a StoreTrap trap
Instruction can cause an Overflow trap
Interruptible instruction
S
O
I
A
D
T
Instruction can be aborted and later restarted.
Instruction can deschedule
Instruction can timeslice
Table 6.2 Instruction features
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6.3 Instruction set tables
Function Memory Mnemonic
Processor Name
cycles
Notes
code
code
0X
1X
2X
3X
4X
5X
6X
7X
8X
9X
AX
BX
CX
DX
EX
FX
0
j
7
jump
D, T
1
ldlp
pfix
ldnl
ldc
ldnlp
nfix
ldl
1
load local pointer
prefix
2
0 to 3
3
1
load non-local
load constant
load non-local pointer
negative prefix
load local
4
1
5
1
6
0 to 3
7
1
8
adc
call
cj
2 to 3
add constant
call
O
9
8
A
B
C
D
E
F
1 or 7
conditional jump
adjust workspace
equals constant
store local
ajw
eqc
stl
2
1
1
2
0
stnl
opr
store non-local
operate
Table 6.3 Primary functions
Memory
code
Mnemonic
Processor Name
cycles
Notes
22FA
23FE
23FD
21F8
testpranal
saveh
savel
sthf
1
3
3
1
1
1
1
2
1
1
test processor analyzing
save high priority queue registers
save low priority queue registers
store high priority front pointer
store high priority back pointer
store low priority front pointer
store low priority back pointer
store timer
25F0
sthb
21FC
21F7
stlf
stlb
25F4
sttimer
lddevid
2127FC
27FE
load device identity†
ldmemstartval
load value of MemStart address
†See Section 22
Table 6.4 Processor initialization operation codes
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Memory Mnemonic
code
Processor
cycles
Name
Notes
24F6
24FB
23F3
23F2
24F1
24F0
and
or
1
1
1
1
1
1
and
or
xor
not
shl
shr
exclusive or
bitwise not
shift left
shift right
F5
FC
add
2
add
A, O
A, O
A, O
A, O
A, O
A, O
A
sub
2
subtract
25F3
27F2
22FC
21FF
F9
mul
3
multiply
fmul
div
5
fractional multiply
divide
4 to 35
rem
gt
3 to 35
remainder
2
greater than
greater than unsigned
difference
25FF
F4
gtu
2
A
diff
1
1
25F2
F8
sum
prod
satadd
satsub
satmul
sum
3
product
A
A
A
A
26F8
26F9
26FA
2 to 3
2 to 3
4
saturating add
saturating subtract
saturating multiply
Table 6.5 Arithmetic/logical operation codes
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ST20-GP1
Memory Mnemonic
Processor
cycles
Name
Notes
code
21F6
23F8
23F7
24FF
23F1
21FA
23F6
23F5
21F9
26F4
26F5
ladd
lsub
lsum
ldiff
2
long add
A, O
A, O
2
long subtract
long sum
1
1
long diff
lmul
ldiv
4
long multiply
A
A, O
A
3 to 35
long divide
lshl
2
2
3
4
4
long shift left
lshr
long shift right
normalize
A
norm
slmul
sulmul
A
signed long multiply
signed times unsigned long multiply
A, O
A, O
Table 6.6 Long arithmetic operation codes
Memory Mnemonic
code
Processor
cycles
Name
Notes
F0
rev
1
reverse
23FA
25F6
21FD
24FC
24F2
25FA
27F9
68FD
xword
cword
xdble
csngl
mint
3
extend to word
check word
A
2 to 3
A, E
1
2
1
1
1
2
extend to double
check single
A, E
minimum integer
duplicate top of stack
pop processor stack
reboot
dup
pop
reboot
Table 6.7 General operation codes
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Memory Mnemonic
code
Processor
cycles
Name
Notes
F2
FA
bsub
wsub
wsubdb
bcnt
wcnt
lb
1
1
1
1
1
1
2
byte subscript
word subscript
form double word subscript
byte count
28F1
23F4
23FF
F1
word count
load byte
23FB
sb
store byte
24FA
move
move message
I
Table 6.8 Indexing/array operation codes
Memory Mnemonic
code
Processor
cycles
Name
Notes
22F2
22FB
24FE
25F1
24F7
22FE
ldtimer
tin
1
load timer
timer input
I
D, I
I
talt
3
timer alt start
timer alt wait
enable timer
disable timer
taltwt
enbt
dist
1 to 7
Table 6.9 Timer handling operation codes
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ST20-GP1
Memory Mnemonic
code
Processor
cycles
Name
Notes
F7
in
input message
output message
output word
D
D
D
D
FB
out
FF
outword
outbyte
FE
output byte
24F3
24F4
24F5
alt
2
3 to 6
8
alt start
alt wait
alt end
altwt
altend
D
24F9
23F0
enbs
diss
1 to 2
1
enable skip
disable skip
21F2
24F8
22FF
resetch
enbc
3
reset channel
enable channel
disable channel
1 to 4
1 to 6
disc
Table 6.10 Input and output operation codes
Memory Mnemonic
code
Processor
cycles
Name
Notes
22F0
21FB
23FC
F6
ret
2
1
return
ldpi
load pointer to instruction
general adjust workspace
general call
gajw
gcall
lend
2 to 3
6
22F1
4 to 5
loop end
T
Table 6.11 Control operation codes
Memory Mnemonic
code
Processor
cycles
Name
Notes
FD
F3
startp
endp
runp
5 to 6
start process
end process
4 to 6
D
23F9
21F5
21FE
3
2
1
run process
stopp
ldpri
stop process
load current priority
Table 6.12 Scheduling operation codes
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Memory Mnemonic
code
Processor
cycles
Name
Notes
21F3
24FD
22F9
21F0
25F5
25F7
25F8
25F9
csub0
2
check subscript from 0
check count from 1
test error false and clear
set error
A, E
A, E
ccnt1
2
testerr
1
seterr
1
stoperr
clrhalterr
sethalterr
testhalterr
1 to 3
stop on error (no error)
clear halt-on-error
set halt-on-error
D
2
1
1
test halt-on-error
Table 6.13 Error handling operation codes
Memory Mnemonic
code
Processor
cycles
Name
Notes
25FB
25FC
25FD
25FE
move2dinit
1
initialize data for 2D block move
2D block copy
move2dall
I
I
I
move2dnonzero
move2dzero
2D block copy non-zero bytes
2D block copy zero bytes
Table 6.14 2D block move operation codes
Memory Mnemonic
code
Processor
cycles
Name
Notes
27F4
27F5
crcword
crcbyte
34
10
calculate crc on word
calculate crc on byte
A
A
27F6
27F7
27F8
bitcnt
3
1
2
count bits set in word
reverse bits in word
A
A
bitrevword
bitrevnbits
reverse bottom n bits in word
Table 6.15 CRC and bit operation codes
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Memory Mnemonic
Processor
cycles
Name
Notes
code
27F3
29FC
26F3
26FD
26FC
cflerr
2
check floating point error
E
fptesterr
unpacksn
roundsn
postnormsn
1
4
load value true (FPU not present)
unpack single length floating point number
round single length floating point number
A
A
A
7
7 to 8
post-normalize correction of single length float-
ing point number
27F1
ldinf
load single length infinity
Table 6.16 Floating point support operation codes
Memory Mnemonic
code
Processor Name
cycles
Notes
2CF7
2CFC
2BFA
2BFB
2FFA
2FFB
2FF8
2BF8
cir
2 to 4
2 to 4
2 to 3
2 to 3
2 to 3
2 to 3
2
check in range
A, E
A, E
A, E
A, E
A, E
A, E
A
ciru
cb
check in range unsigned
check byte
cbu
check byte unsigned
check sixteen
cs
csu
check sixteen unsigned
sign extend sixteen to word
sign extend byte to word
xsword
xbword
3
A
Table 6.17 Range checking and conversion instructions
Memory Mnemonic
code
Processor Name
cycles
Notes
2CF1
2CFA
2CF8
2BF9
2FF9
ssub
ls
1
1
2
1
1
sixteen subscript
load sixteen
ss
store sixteen
lbx
lsx
load byte and sign extend
load sixteen and sign extend
Table 6.18 Indexing/array instructions
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Memory Mnemonic
code
Processor Name
cycles
Notes
2FF0
2FF2
2FF4
62F4
2FF1
2FF3
2FF5
devlb
3
3
3
device load byte
A
A
A
I
devls
device load sixteen
device load word
device move
devlw
devmove
devsb
devss
devsw
3
3
3
device store byte
device store sixteen
device store word
A
A
A
Table 6.19 Device access instructions
Memory
code
Mnemonic
Processor Name
cycles
Notes
60F5
60F4
wait
4 to 10
6 to 10
wait
D
signal
signal
Table 6.20 Semaphore instructions
Memory Mnemonic
code
Processor Name
cycles
Notes
60F0
60F1
60F2
60F3
60FC
60FD
62FE
62FF
61FF
2BF0
2CF4
2CF5
2CFD
2CFE
swapqueue
swaptimer
insertqueue
timeslice
ldshadow
stshadow
restart
3
swap scheduler queue
swap timer queue
insert at front of scheduler queue
timeslice
5
1 to 2
3 to 4
6 to 23
load shadow registers
store shadow registers
restart
A
A
5 to 17
19
causeerror
iret
2
cause error
3 to 9
interrupt return
settimeslice
intdis
1
1
2
2
2
set timeslicing status
interrupt disable
intenb
interrupt enable
gintdis
global interrupt disable
global interrupt enable
gintenb
Table 6.21 Scheduling support instructions
43/116
ST20-GP1
Memory Mnemonic
Processor Name
cycles
Notes
code
26FE
2CF6
2CFB
26FF
60F7
60F6
60FB
ldtraph
ldtrapped
sttrapped
sttraph
trapenb
trapdis
tret
11
11
11
11
2
load trap handler
L
L
load trapped process status
store trapped process status
store trap handler
trap enable
S
S
2
trap disable
9
trap return
Table 6.22 Trap handler instructions
Memory Mnemonic
code
Processor Name
cycles
Notes
68FC
63F0
ldprodid
nop
1
1
load product identity
no operation
Table 6.23 Processor initialization and no operation instructions
Memory Mnemonic
code
Processor Name
cycles
Notes
64FF
64FE
64FD
64FC
clockenb
clockdis
ldclock
2
2
1
2
clock enable
clock disable
load clock
stclock
store clock
Table 6.24 Clock instructions
44/116
ST20-GP1
7 Memory map
The ST20-GP1 processor memory has a 32-bit signed address range. Words are addressed by
30-bit word addresses and a 2-bit byte-selector identifies the bytes in the word. Memory is divided
into 4 banks which can each have different memory characteristics and can be used for different
purposes. In addition, on-chip peripherals can be accessed via the device access instructions (see
Table 6.19).
Various memory locations at the bottom and top of memory are reserved for special system
purposes. There is also a default allocation of memory banks to different uses.
Note that the ST20-GP1 uses 30 bits of addressing internally, but addresses A20-A29 are not
brought out to external pins. Address bits A30 and A31 are used as bank selects.
7.1 System memory use
The ST20-GP1 has a signed address space where the address ranges from MinInt (#80000000)
at the bottom to MaxInt (#7FFFFFFF) at the top. The ST20-GP1 has an area of 4 Kbytes of RAM
at the bottom of the address space provided by on chip memory. The bottom of this area is used to
store various items of system state. These addresses should not be accessed directly but via the
appropriate instructions.
Near the bottom of the address space there is a special address MemStart. Memory above this
address is for use by user programs while addresses below it are for private use by the processor
and used for subsystem channels and trap handlers. The address of MemStart can be obtained
via the ldmemstartval instruction.
7.1.1 Subsystem channels memory
Each DMA channel between the processor and a subsystem is allocated a word of storage below
MemStart. This is used by the processor to store information about the state of the channel. This
information should not normally be examined directly, although debugging kernels may need to do
so.
Boot channel
The subsystem channel which is a link input channel is identified as a ‘boot channel’. When the
processor is reset, and is set to boot from link, it waits for boot commands on this channel.
7.1.2 Trap handlers memory
The area of memory reserved for trap handlers is broken down hierarchically. Full details on trap
handlers is given in see Section 4.6 on page 23.
•
•
Each high/low process priority has a set of trap handlers.
Each set of trap handlers has a handler for each of the four trap groups (refer to Section
4.6.1).
•
•
Each trap group handler has a trap handler structure and a trapped process structure.
Each of the structures contains four words, as detailed in Section 4.6.3.
The contents of these addresses can be accessed via ldtraph, sttraph, ldtrapped and sttrapped
instructions.
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ST20-GP1
7.2 Boot ROM
When the processor boots from ROM, it jumps to a boot program held in ROM with an entry point 2
bytes from the top of memory at #7FFFFFFE. These 2 bytes are used to encode a negative jump
of up to 256 bytes down in the ROM program. For large ROM programs it may then be necessary
to encode a longer negative jump to reach the start of the routine.
7.3 Internal peripheral space
On-chip peripherals are mapped to addresses in the top half of memory bank 2 (address range
#20000000 to #3FFFFFFF). They can only be accessed by the device access instructions (see
Table 6.19). When used with addresses in this range, the device instructions access the on-chip
peripherals rather than external memory. For all other addresses the device instructions access
memory. Standard load/store instructions to these addresses will access external memory.
This area of memory is allocated to peripherals in 4K blocks, see the following memory map.
46/116
ST20-GP1
MEMORY
BANK
ADDRESS
USE
MaxInt #7FFFFFFF
BootEntry #7FFFFFFE Boot entry point
Bank 3
↑
User code/Data/Stack and Boot ROM
#40000000
↑
RESERVED
#2000E000
↑
DSP controller peripheral
(registers accessed via CPU device accesses)
#2000C000
↑
Parallel port controller peripheral
(registers accessed via CPU device accesses)
#2000A000
↑
PIO controller peripheral
(registers accessed via CPU device accesses)
#20008000
↑
ASC1 controller peripheral
(registers accessed via CPU device accesses)
Bank 2
#20006000
↑
ASC0 controller peripheral
(registers accessed via CPU device accesses)
#20004000
↑
EMI controller peripheral
(registers accessed via CPU device accesses)
#20002000
↑
Interrupt and low power controller peripheral
(registers accessed via CPU device accesses)
#20000000
↑
External peripherals or memory
User code/Data/Stack
#00000000
↑
Bank 1
#C0000000
↑
Start of external memory #80001000
↑
MemStart #80000140
#80000130 Low priority Scheduler trapped process
#80000120 Low priority Scheduler trap handler
#80000110 Low priority SystemOperations trapped process
#80000100 Low priority SystemOperations trap handler
#800000F0 Low priority Error trapped process
#800000E0 Low priority Error trap handler
Bank 0
#800000D0 Low priority Breakpoint trapped process
#800000C0 Low priority Breakpoint trap handler
#800000B0 High priority Scheduler trapped process
#800000A0 High priority Scheduler trap handler
Figure 7.1 ST20-GP1 memory map
47/116
ST20-GP1
MEMORY
BANK
ADDRESS
USE
#80000090 High priority SystemOperations trapped process
#80000080 High priority SystemOperations trap handler
#80000070 High priority Error trapped process
#80000060 High priority Error trap handler
#80000050 High priority Breakpoint trapped process
TrapBase #80000040 High priority Breakpoint trap handler
#8000003C
↑
RESERVED
Bank 0
#8000001C
#80000018 Byte wide parallel port input DMA channel
#80000014 DSP module DMA channel
#80000010 Link0 (boot) input channel
#8000000C RESERVED
#80000008 Byte wide parallel port output DMA channel
#80000004 RESERVED
MinInt #80000000 Link0 output channel
Figure 7.1 ST20-GP1 memory map
48/116
ST20-GP1
8 Memory subsystem
The memory system consists of SRAM and a programmable memory interface. The specific details
on the operation of the memory interface are described separately in Chapter 9.
8.1 SRAM
There is an internal memory module of 4 Kbytes of SRAM. The internal SRAM is mapped into the
base of the memory space from MinInt (#80000000) extending upwards, as shown in Figure 8.1.
This memory can be used to store on-chip data, stack or code for time critical routines.
External
memory
#80001000
SRAM
MinInt #80000000
Figure 8.1 SRAM mapping
Where internal memory overlays external memory, internal memory is accessed in preference.
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ST20-GP1
9 Programmable memory interface
The ST20-GP1 programmable memory interface provides glueless support for up to four banks of
SRAM or ROM memory. Sufficient configuration options are provided to enable the interface to be
used with a wide variety of SRAM speeds, permitting systems to be built with optimum price/
performance trade-offs.
Although designed primarily for SRAM-like memory devices, the configurability enables glueless
connection to other peripheral devices such as FIFOs and UARTs.
The programmable memory interface is also referred to as the external memory interface (EMI).
The EMI provides configuration information for four independent banks of external memory
devices. The addresses of these bank boundaries are hard wired to give each bank one quarter of
the address space of the machine. Bank 0 occupies the lowest quarter of the [signed] address
space, bank 3 is the highest, see Figure 9.1. Each bank can contain up to 1 Mbyte of external
memory.
7FFFFFFF
40000000
On-chip peripheral registers (including the EMI
configuration registers) are mapped into the upper
half of this bank.
3FFFFFFF
On-chip peripheral
registers
20000000
1FFFFFFF
00000000
FFFFFFFF
80000FFF
Internal
C0000000
BFFFFFFF
SRAM
MemStart
Traps/
exceptions
Internal SRAM
80000000
Subsystem
channels
80000000
Addresses shown are physical addresses.
Figure 9.1 Memory allocation
50/116
ST20-GP1
9.1 EMI signal descriptions
The following section describes the functions of the EMI pins. Note that a signal name prefixed by
not indicates active low.
MemAddr1-19
External address bus. The ST20-GP1 uses 30 bits of addressing internally but only the bottom 18
bits are brought out to external pins (MemAddr2-19); MemAddr1 is generated by the EMI.
MemAddr1-19 is valid and constant for the whole duration of an external access. The memory
locations in each bank can be accessed at multiple addresses, as bits 20-29 are ignored when
making external accesses.
MemData0-15
External data bus. The data bus may be configured to be either 8 or 16 bits wide on a per bank
basis. MemData0 is always the least significant bit. MemData7 is the most significant bit in 8-bit
mode and MemData15 is the most significant bit in 16-bit mode. When performing a write access
to a bank configured to be 8-bits wide, MemData8-15 are held in a high-impedance state for the
duration of the access; MemData0-7 behave according to the configuration parameters as
specified in Section 9.5. When making a write to a bank configured to be 16-bits wide,
MemData0-15 behave according to the configuration parameters.
notMemCE0-3
Chip enable strobes, one per bank. The notMemCE0-3 strobe corresponding to the bank being
accessed will be active on both reads and writes to that bank.
notMemOE3-0
Output enable strobes, one per bank. The notMemOE0-3 strobe corresponding to the bank being
accessed will be active only on reads to that bank.
notMemWB0-1
Byte selector strobes to select bytes within a 16-bit half-word. These strobes are shared between
all four banks. notMemWB0 always corresponds to write data on MemData0-7 whether the bus is
currently 8 or 16 bits wide. When the EMI is writing to a bank configured to be 16 bits wide,
notMemWB1 corresponds to MemData8-15. When the EMI is accessing a bank configured to be
8 bits wide, notMemWB1 becomes address bit 0 and follows the timing of MemAddr1-19 for that
bank.
MemWait
Halt external access. The EMI samples MemWait at or just after the midpoint of an access. If
MemWait is sampled high, the access is stalled. MemWait will then continue to be sampled and
the access proceeds when MemWait is sampled low. The action of MemWait may be disabled by
software, see Section 9.4. No mechanism is provided to abort an access; if MemWait is held high
too long the EMI will become a contentious resource and may stall the ST20-GP1.
BootSource0-1
These signals are sampled immediately after reset and determine both the bootstrap behavior and
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ST20-GP1
the initial bus width of all banks after reset.
BootSource[1:0] Bootstrap start-up conditions
00
01
10
11
Boot from link. 16-bit bus width for all banks.
Boot from ROM. 8-bit bus width for all banks. Link operational.
Boot from ROM. 16-bit bus width for all banks. Link powered down.
Boot from ROM. 8-bit bus width for all banks. Link powered down.
Table 9.1 BootSource0-1 encoding
9.2 Strobe allocation
Pin
Bank allocation Correspondence Active access type
notMemCE0-3 1 per bank
0
1
2
3
bank 0
bank 1
bank 2
bank 3
Reads and writes
notMemOE0-3 1 per bank
0
1
2
3
bank 0
bank 1
bank 2
bank 3
Reads only
notMemWB0
notMemWB1
Shared amongst MemData0-7
all banks.
Writes only. Indicates valid write data on MemData0-7.
Writes only. Indicates valid write data on MemData8-15.
Shared amongst 16-bit bus:
all banks.
MemData8-15
8-bit bus:
Reads and writes. Behaves as address bit 0 with same
not applicable
timing as MemAddr1-19.
Table 9.2 Strobe allocation
9.3 External accesses
The EMI differentiates accesses and transactions. An access is the lowest denominator of a
transaction. Since the ST20 word size is 32 bits, several accesses are required to complete a
transaction in most cases. The following are cases where several accesses may not be required:
•
CPU executes a sb (store byte), lb (load byte) or ss (store sixteen), ls (load sixteen) instruc-
tion.
•
CPU is executing a move2dnonzero (2D block copy non-zero bytes) or move2dzero (2D
block copy zero bytes) instruction and the data dictates that certain bytes are not to be
written.
•
The first or last DMA operation to or from a link is to a non word aligned byte address.
Figure 9.2 shows the generic EMI activity during a read access and the configurable parameters.
The rising edge of notMemOE always occurs at the end of the read access just after the data is
latched on chip. notMemWB0 is always inactive during a read access. notMemWB1 activity
during a read access depends on the bus width for the bank. The strobe is inactive if the bus width
is configured to be 16-bit. If the bus width is configured to be 8-bit, notMemWB1behaves as
address bit 0 with the same timing as MemAddr1-19.
52/116
ST20-GP1
Access duration
MemAddr1-19
notMemWB1*
(MemAddr0)
CEe1 time
OEe1 time
CEe2 time
notMemCE
notMemOE
BusRelease time
MemData0-7
MemData8-15†
Read data latched
on chip
* Only when bus width is 8-bit. Inactive when bus width is 16-bit.
† Ignored when bus width is 8-bit.
Figure 9.2 Configuration parameters for a read access
53/116
ST20-GP1
Figure 9.3 shows the generic EMI activity during a write access. notMemOE is inactive during a
write access, and the function of notMemWB1 is dictated by the bus width of the bank in the same
way as for a read access. MemData8-15 is held in high impedance during a write access if the bus
width is 8-bit, otherwise it follows the timing configured for MemData0-7.
Access duration
MemAddr1-19
notMemWB1*
(MemAddr0)
CEe1 time
WBe1 time
CEe2 time
WBe2 time
notMemCE
notMemWB0
Data drive delay
MemData0-7
MemData8-15†
* Only when bus width is 8-bit. When bus width is 16-bit, notMemWB1 follows the timing
specified for notMemWB0.
† Held in high impedance when bus width is 8-bit.
Figure 9.3 Configuration parameters for a write access
The following caveats relate to strobe edge programming:
•
If any of the strobe edges are programmed to occur outside the period defined by Access-
Duration, the activity for that strobe is undefined.
•
If a strobe’s rising and falling edges are programmed to occur on the same system clock
edge, they will nullify each other and the strobe will stay in the same state. This rule also
applies for consecutive accesses.
Transactions normally consist of several accesses which run consecutively without any ‘dead
cycles’. The number of accesses in a transaction is dependent on the bus width and the nature of
the memory bus request. Table 9.3 lists the transaction composition and the behavior of
MemAddr1 and notMemWB0-1 for each access.
54/116
ST20-GP1
Bus
width
Valid
bytes
<3:0>
Number of
accesses
required
MemAddr1
notMemWB1
notMemWB0
1
2
3
4
1
2
3
4
1
2
3
4
8
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
0001
0010
0011
0100
0101
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
1
1
2
1
2
2
3
1
2
2
3
2
3
3
4
1
1
1
1
2
2
2
1
2
2
2
1
2
2
2
L
L
L
H
L
L
L
H
L
L
L
H
L
L
L
L
L
L
H
L
L
L
H
L
L
L
H
L
L
L
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
H
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
L
H
L
L
L
H
L
H
L
H
L
L
L
H
L
I
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
H
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
I
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
A
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
8
-
-
-
-
-
-
8
L
-
-
H
-
-
A
-
-
8
-
-
-
8
H
H
L
-
-
L
L
H
-
-
A
A
A
-
-
8
-
-
-
8
H
-
L
-
A
-
8
8
H
H
L
H
H
H
L
-
-
H
H
H
H
L
L
H
-
-
A
A
A
A
A
A
A
-
-
8
-
-
-
8
H
-
H
-
A
-
8
8
H
H
H
-
H
H
L
-
A
A
A
-
8
8
16
16
16
16
16
16
16
16
16
16
16
16
16
16
16
-
-
A
A
I
-
-
-
-
-
-
-
-
A
A
A
I
-
-
-
-
-
-
-
-
H
H
H
-
-
I
I
-
A
A
A
-
-
-
A
A
A
I
I
-
-
-
I
-
A
I
-
-
-
-
-
H
H
H
-
-
A
A
A
-
-
A
I
I
-
-
A
A
A
I
-
I
-
-
-
A
A
A
I
I
-
-
-
-
-
H
H
H
-
A
A
A
-
A
A
A
-
-
A
A
-
-
-
-
A
-
Table 9.3 Transaction composition for valid bytes on internal memory bus
Key: L = low for whole access
H = high for whole access
A = active on write accesses
I = inactive for whole access
The EMI buffers subsequent transactions which may occur, without intervening dead cycles except
55/116
ST20-GP1
in the following two cases:
•
The previous access was a read and the pending one is a write. The write access will not
start until the programmed number of BusReleaseTime cycles have elapsed.
•
The previous access was to a different bank to the pending access (bank switch). One
cycle is always inserted between accesses to different banks. Note that, if the first condition
is also true, further cycles may be inserted to account for BusReleaseTime.
The first case may be optimized slightly by making use of the DataDriveDelay configuration
register parameter, see Table 9.4. When this is used, the programmed BusReleaseTime may be
smaller, reducing the number of dead cycles, see Figure 9.4.
Read
Read
Write
Case 1. DataDriveDelay set
to zero. All dead time taken up
by BusReleaseTime.
Read data
Write data
BusRelease
time
Case 2. DataDriveDelay
used to absorb some
BusReleaseTime. Dead time
may be reduced.
Write
Read data
Write data
DataDriveDelay
BusRelease
time
Figure 9.4 Use of DataDriveDelay parameter
Note, if DataDriveDelay is used, it must be used for all banks. If this rule is not adhered to, bus
contention may occur on bank switches. For example, consider case 2 in Figure 9.4 above. If the
BusReleaseTime coincides with the dead cycle inserted due to a bank switch, contention will
occur unless DataDriveDelay is programmed in the same way as if no bank switch had occurred.
9.4 MemWait
When enabled (see Table 9.4), MemWait is sampled at the midpoint of accesses which are
configured to be four cycles or greater. If the duration of the external access is not an even number
of cycles (i.e. the AccessDuration bit field in the EMIConfigData register, see Table 9.4, is an odd
number), MemWait is sampled on the internal rising clock edge just after the midpoint of the
access.
Once a high has been sampled, the access is stalled. MemWait suspends the state of the EMI in
the cycle after it is sampled high. The state remains suspended until MemWait is sampled low. Any
strobe edges scheduled to occur in the cycle after MemWait is sampled will not occur. Strobe
edges scheduled to occur on the same edge as MemWait is sampled are not affected. Figure 9.5
and Figure 9.6 show the extension of the external memory cycle and the delaying of strobe
56/116
ST20-GP1
transitions. Note, the clock shown in the figures is the internal on-chip clock and is provided as a
guide to show the minimum setup time of MemWait relative to the strobes.
clock
MemWait
Strobe1
Strobe2
Strobe3
Figure 9.5 Strobe activity without MemWait
MemWait
asserted
wait
cycle
clock
MemWait
Strobe1
Strobe2
Strobe3
Figure 9.6 Strobe activity with MemWait
57/116
ST20-GP1
9.5 EMI configuration registers
Configuration parameters are stored in registers which are mapped into the device address space.
They may be accessed using devsw (device store word) and devlw (device load word) instructions.
The base addresses for the EMI registers are given in the Memory Map chapter.
EMIConfigData0-3 registers
The EMIConfigData0-3 registers contain configuration data for each of the EMI banks. The format
of each of the EMIConfigData0-3 registers is identical and is shown in Table 9.4.
EMIConfigData0-3
EMI base address + #00, #04, #08, #0C
Function
Read/Write
Units
Bit
Bit field
0
MemWaitEnable
DataDriveDelay
BusWidth
Enables the MemWait pin.
-
Phases
-
3:1
4
Drive delay of data bus for writes.
Bus width of the bank (8 or 16 bits).
BusWidth
Bank width
16 bits
8 bits
0
1
8:5
AccessDuration
BusReleaseTime
CEe1Time
Duration of the external access.
Cycles
Cycles
Phases
Phases
Phases
Phases
Phases
-
10:9
14:11
18:15
22:19
26:23
30:27
31
Duration bus release time.
Delay from access start to notMemCE falling edge.
Delay from notMemCE rising edge to end of access.
Delay from access start to notMemOE falling edge.
Delay from access start to notMemWB falling edge.
Delay from notMemWB rising edge to end of access.
Reserved
CEe2Time
OEe1Time
WBe1Time
WBe2Time
Table 9.4 EMIConfigData0-3 register format - 1 per bank
EMIConfigLock register
The EMIConfigLock register is provided to write protect the EMIConfigData0-3 registers (further
writes to these registers are ignored). This bit is set by performing a devsw instruction to the given
address; the write data is ignored.
This register, once set, can only be cleared by resetting the ST20-GP1.
EMIConfigLock
EMI base address + #10
Function
Write only
Bit
Bit field
ConfigLock
0
When set, the EMIConfigData0-3 registers are read only.
Table 9.5 EMIConfigLock register format
EMIConfigStatus register
The EMIConfigStatus register is provided to indicate which registers have been written to and the
58/116
ST20-GP1
status of the lock and stall bits. Table 9.6 shows the format of the EMIConfigStatus register.
EMIConfigStatus
Bit Bit field
EMI base address + #20
Read only
Function
0
1
WrittenBank0
Bank 0 configuration has been written to using a devsw instruction.
Bank 1 configuration has been written to using a devsw instruction.
Bank 2 configuration has been written to using a devsw instruction.
Bank 3 configuration has been written to using a devsw instruction.
EMIConfigData0-3 registers are write protected.
EMIConfigStall has been set.
WrittenBank1
WrittenBank2
WrittenBank3
WriteLock
2
3
4
5
MemStall
31:6
Reserved
Table 9.6 EMIConfigStatus register format
EMIConfigStall register
The EMIConfigStall register can be used to stall the EMI. When set it prevents the EMI from
accepting further requests from the CPU or communications subsystems. Its main use is intended
to be in systems which anticipate turning the power off; the EMI must be inactive during such an
event, otherwise battery backed memory may be corrupted.
This register, once set, can only be cleared by resetting the ST20-GP1.
EMIConfigStall
EMI base address + #30
Function
Write only
Bit
Bit field
EMIStall
0
When set, this bit prevents the arbiter from granting any more accesses to the
memory subsystem.
Table 9.7 EMIConfigStall register format
9.6 Reset and bootstrap behavior
Table 9.8 shows the state of the EMI signals during reset. MemAddr2-19 are driven with a copy of
the value on the internal memory bus2-19.
Pins
Value
MemAddr2-19
MemAddr1
Valid
High
notMemCE0-3
notMemOE0-1
notMemWB0-1
MemData0-15
All high
All high
All high
High impedance
Table 9.8 EMI signal values during reset
Table 9.9 shows the configuration values for all banks during and after reset. If the BootSource0-1
pins indicate that the ST20-GP1 will boot from ROM, the BusWidth is set to the correct value as
the ST20-GP1 comes out of reset.
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ST20-GP1
Parameter
Bits Value during and after reset
Units
BusWidth
1
1
1
4
4
4
4
4
4
2
3
Depends on BootSource0-1 pins (see Table 9.1, page 52).
-
MemWaitEnable
BankReadOnly
AccessDuration
CEe1Time
1 (Enabled)
-
0 (Read/Write)
1010 (10 cycles)
0000
-
Cycles
Phases
Phases
Phases
Phases
Phases
Cycles
Phases
CEe2Time
0000
OEe1Time
0000
WBe1Time
1001 (9 phases; 4.5 cycles)
0010 (2 phases; 1 cycle)
10 (2 cycles)
WBe2Time
BusReleaseTime
DataDriveDelay
101 (5 phases; 2.5 cycles)
Table 9.9 Configuration register values during reset
The behavior of the ST20-GP1 after reset depends upon the value on the BootSource0-1 pins. In
all cases, the EMI is loaded with a slow default configuration which is suitable for performing
accesses to ROM and SRAM (see Figure 9.7).
10 cycles
MemAddr1-19
notMemCE
notMemOE
2 phases (1 cycle)
9 phases (4.5 cycles)
notMemWB0-1
2 cycles
MemData0-15
(read)
5 phases
MemData0-15
(write)
Figure 9.7 Default configuration
When booting from ROM, the first EMI access will be an instruction fetch from bank 3. When
booting from a link, the bootstrap is loaded into the ST20-GP1 internal SRAM located logically at
the bottom of bank 0.
The default bus width for all banks is set at reset by reading the value on the BootSource0-1 pins
(see Table 9.1). If this bus width is inappropriate for a particular bank, then configuration software
must change it before it is accessed, otherwise some memory locations will contain indeterminate
contents. Note, particular care must be paid to instruction fetching behavior of the CPU. It is
important to match the program memory with the correct bus width using BootSource0-1.
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ST20-GP1
10 Clocks and low power controller
10.1 Clocks
An on-chip phase locked loop (PLL) generates all the internal high frequency clocks. The PLL is
used to generate the internal clock frequencies needed for the CPU and the Link. Alternatively a
direct clock input can provide the system clocks. The single clock input (ClockIn) must be
16.368 MHz for PLL operation for GPS.
The internal clock may be turned off (including the PLL) enabling power down mode.
The ST20-GP1 can be set to operate in TimesOneMode, which is when the PLL is bypassed.
During TimesOneMode the input clock must be in the range 0 to 30 MHz and should be nominally
50/50 mark space ratio.
10.1.1 Speed select
The speed of the internal processor clock is variable in discrete steps. The clock rate at which the
ST20-GP1 runs is determined by the logic levels applied on the two speed select lines
SpeedSelect0-1 as detailed in Table 10.1. The frequency of ClockIn (fclk) for the speeds given in
the table is 16.368 MHz.
The SysRatio register, see Table 10.9, gives the speed at which the system PLL is running. It
contains the relevant PLL multiply ratio when using the PLL, or contains the value ‘1’ when in
TimesOneMode for the PLL.
SpeedSelect1
SpeedSelect0
Processor clock
speed (MHz)
Processor
cycle time (ns)
approximate
Phase lock loop
factor (PLLx)
Link speed
(Mbits/s)
0
0
1
1
0
1
0
1
TimesOneMode
61.0
0.4 x fclk
19.641
19.641
16.368
32.736
1
2
30.5
RESERVED
Table 10.1 Processor speed selection
10.2 Low power control
The ST20-GP1 is designed for 0.5 micron, 3.3V CMOS technology and runs at speeds of up to
32.736 MHz. 3.3V operation provides reduced power consumption internally and allows the use of
low power peripherals. In addition, to further enhance the potential for battery operation, a low
power power-down mode is available.
The different power levels of the ST20-GP1 are listed below.
•
•
Operating power — power consumed during functional operation.
Stand-by power — power consumed during little or no activity. The CPU is idle but ready to
immediately respond to an interrupt/reschedule.
•
Power-down — internal clocks are stopped and power consumption is significantly reduced.
Functional operation is stalled. Normal functional operation can be resumed from previous
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ST20-GP1
state as soon as the clocks are stable. All internal logic is static so no information is lost
during power down.
•
Power to most of the chip removed — only the real time clock supply (RTCVDD) power on.
10.2.1 Power-down mode
The ST20-GP1 enters power-down when:
•
the low power alarm is programmed and started, via configuration registers, providing there
are no interrupts pending.
The ST20-GP1 exits power-down when:
•
•
an unmasked interrupt becomes pending.
the low power alarm counter reaches zero.
In power-down mode the processor and all peripherals are stopped, including the external memory
controller and optionally the PLL. Effectively the internal clock is stopped and functional operation
is stalled. On restart the clock is restarted and the chip resumes normal functional operation.
10.2.2 Low power mode
Low power mode can be achieved in one of two ways, as listed below.
•
Availability of direct clock input — this allows external control of clocking directly and thus
direct control of power consumption.
•
Internal global system clock may be stopped — in this case the external clock remains run-
ning. This mechanism allows the PLL to be kept running (if desired) so that wake up from
low power mode will be fast.
Wake-up from low power mode can be from: specific external pin activity (Interrupt pin); or the low
power timer alarm.
The low power timer and alarm are provided to control the duration for which the global clock
generation is stopped during low power mode. The timer and alarm registers can be set by the
device store instructions and read by the device load instructions.
Low power timer
The timer keeps track of real time, even when the internal clocks are stopped. The timer is a 64-bit
counter which runs off an external clock (LPClockIn). This clock rate must not be more than one
eighth of the system clock rate.
The real time clock is powered from a separate Vdd (RTCVDD) allowing it to be maintained at
minimal power consumption.
Low power alarm
There is also a 40-bit counter which can be used as a low power alarm or as a watchdog timer, this
is determined by the setting of the WdEnable register, see Table 10.10.
Alarm
A write to the LPAlarmStart register starts the low power alarm counter and the ST20-GP1 enters
low power mode. When the counter has counted down to zero, assuming no other valid wake-up
sources occur first, the ST20-GP1 exits low power mode and the global clocks are turned back on.
Whilst the clocks are turned off the LowPowerStatus pin is high, otherwise it is low.
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ST20-GP1
Watchdog timer
The low power alarm counter is set to operate as a watchdog timer by setting the WdEnable
register to 1. This disables entering low power mode when starting the timer. The low power alarm
is programmed and started as normal.
The WdFlag register can be read to determine if the device was reset by the notRST input or by a
watchdog time-out.
When the low power alarm counts down to the value #1, the notWdReset pin is asserted low for 1
low power clock cycle. In addition an internal reset of the ST20-GP1 is performed.
10.3 Low power configuration registers
The low power controller is allocated a 4k block of memory in the internal peripheral address
space. Information on low power mode is stored in registers as detailed in the following section.
The registers can be examined and set by the devlw (device load word) and devsw (device store
word) instructions, see Table 6.19 on page 43. Note, they can not be accessed using memory
instructions.
LPTimerLS and LPTimerMS
The LPTimerLS and LPTimerMS registers are the least significant word and most significant word
of the LPTimer register. This enables the least significant or most significant word to be written
independently without affecting the other word.
LPTimerLS
LPC base address + #400
Function
Read/Write
Bit
Bit field
LPTimerLS
31:0
Least significant word of the low power timer.
Table 10.2 LPTimerLS register format
LPTimerMS
LPC base address + #404
Read/Write
Bit
Bit field
LPTimerMS
Function
31:0
Most significant word of the low power timer.
Table 10.3 LPTimerMS register format
When the LPTimer register is written, the low power timer is stopped and the new value is
available to be written to the low power timer.
LPTimerStart
A write to the LPTimerStart register starts the low power timer counter. The counter is stopped
and the LPTimerStart register reset if either counter word (LPTimerLS and LPTimerMS) is
written.
Note, setting the LPTimerStart register to zero does not stop the timer.
LPTimerStart
LPC base address + #408
Function
Write
Bit
Bit field
LPTimerStart
0
A write to this bit starts the low power timer counter.
Table 10.4 LPTimerStart register format
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ST20-GP1
LPAlarmLS and LPAlarmMS
The LPAlarmLS and LPAlarmMS registers are the least significant word and most significant word
of the LPAlarm register. This is used to program the low power alarm.
LPAlarmLS
LPC base address + #410
Function
Read/Write
Bit
Bit field
LPAlarmLS
31:0
Least significant word of the low power alarm.
Table 10.5 LPAlarmLS register format
LPAlarmMS
LPC base address + #414
Read/Write
Bit
Bit field
LPAlarmMS
Function
7:0
Most significant word of the low power alarm.
Table 10.6 LPAlarmMS register format
LPAlarmStart
A write to the LPAlarmStart register starts the low power alarm counter. The counter is stopped
and the LPStart register reset if either counter word (LPTimerLS and LPTimerMS) is written.
LPAlarmStart
LPC base address + #418
Function
Write
Bit
Bit field
LPAlarmStart
0
A write to this bit starts the low power alarm counter.
Table 10.7 LPAlarmStart register format
LPSysPll
The LPSysPll register controls the System Clock PLL operation when low power mode is entered.
This allows a compromise between wake-up time and power consumption during stand-by.
LPSysPll
Bit
LPC base address + #420
Function
Read/Write
Bit field
1:0
LPSysPll
Determines the system clock PLL when low power mode is entered, as follows:
LPSysPll1:0 System clock
00
01
10
11
PLL off
PLL reference on and power on
PLL reference on and power on
PLL on
Table 10.8 LPSysPll register format
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ST20-GP1
SysRatio
The SysRatio register is a read only register and gives the speed at which the system PLL is running.
It contains the relevant PLL multiply ratio when using the PLL, or contains the value ‘1’ when in
TimesOneMode for the PLL.
SysRatio
Bit
LPC base address + #500
Function
Read
Bit field
5:0
SysRatio
PLL speed, as follows:
SysRatio PLL
1
2
4
6
x1
x1
x2
x3
TimesOneMode
16.368 MHz
32.736 MHz
RESERVED
Table 10.9 SysRatio register format
WdEnable
Setting the WdEnable register enables the low power alarm counter to be used as a watchdog
timer.
WdEnable
LPC base address + #510
Function
Read/Write
Bit
Bit field
WdEnable
0
Determines whether the low power alarm is set to operate as an alarm or as a
watchdog timer.
0
1
alarm
watchdog
Table 10.10 WdEnable register format
WdFlag
This register can be used to determine if the device was reset by the notRST input or by a
watchdog time-out.
Note that this bit is not reset by the CPUReset input.
WdFlag
LPC base address + #514
Function
Read
Bit
Bit field
WdFlag
0
Watchdog timer flag.
0
1
set to 0 by an external notRST
set to 1 when the watchdog counter is #1 and the WdEnable register is 1
Table 10.11 WdFlag register format
10.4 Clocking sources
The low power timer and alarm must be clocked at all times by one of the following clocking sources:
•
External clock input (LPClockIn) — this clock must not be more than one eighth of the sys-
tem clock rate. In this case the LPClockOsc pin should not be connected on the board.
•
Watch crystal, as in Figure 10.1.
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ST20-GP1
internal low power clock
LPClockIn
LPClockOsc
A
B
330 KΩ
watch crystal
(32768 Hz)
22 pF
GND
10 pF
GND
A - this node should have very low capacitance < 10 pF.
B - this node must have zero dc load.
Figure 10.1 Watch crystal clocking source
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ST20-GP1
11 System services
The system services module includes the control system, the PLL and power control. System
services include all the necessary logic to initialize and sustain operation of the device and also
includes error handling and analysis facilities.
11.1 Reset, initialization and debug
The ST20-GP1 is controlled by a notRST pin which is a global power-on-reset. The CPU itself can
also be controlled by CPUReset and CPUAnalyse signals separately from the on-chip peripherals.
11.1.1 Reset
notRST initializes the device and causes it to enter its boot sequence which can either be in off-
chip ROM or can be received down a link (see Section 11.2 on bootstrap). notRST must be
asserted at power-on.
When notRST is asserted low, all modules are forced into their power-on reset condition. The
clocks are stopped. The rising edge of notRST is internally synchronized and delayed until the
clocks are stable before starting the initialization sequence.
CPUReset is provided as a functional reset which is quicker to reboot as the PLL is not reset. In
other respects the effect is the same as notRST. CPUReset can be used in conjunction with
CPUAnalyse.
11.1.2 CPUAnalyse
If CPUAnalyse is taken high when the ST20-GP1 is running, the ST20-GP1 will halt at the next
descheduling point. CPUReset may then be asserted. When CPUReset comes low again the
ST20-GP1 will be in its reset state, and information on the state of the machine when it was halted
by the assertion of CPUAnalyse, is maintained permitting analysis of the halted machine.
An input link will continue with outstanding transfers. An output link will not make another access to
memory for data but will transmit only those bytes already in the link buffer. Providing there is no
delay in link acknowledgment, the link will be inactive within a few microseconds of the ST20-GP1
halting.
If CPUAnalyse is taken low without CPUReset going high the processor state and operation are
undefined.
11.1.3 Errors
Software errors, such as arithmetic overflow or array bounds violation, can cause an error flag to be
set. This flag is directly connected to the ErrorOut pin. The ST20-GP1 can be set to ignore the
error flag in order to optimize the performance of a proven program. If error checks are removed
any unexpected error then occurring will have an arbitrary undefined effect. The ST20-GP1 can
alternatively be set to halt-on-error to prevent further corruption and allow postmortem debugging.
The ST20-GP1 also supports user defined trap handlers, see Section 4.6 on page 23 for details.
If a high priority process pre-empts a low priority one, status of the Error and HaltOnError flags is
saved for the duration of the high priority process and restored at the conclusion of it. Status of both
flags is transmitted to the high priority process. Either flag can be altered in the process without
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ST20-GP1
upsetting the error status of any complex operation being carried out by the pre-empted low priority
process.
In the event of a processor halting because of HaltOnError, the link will finish outstanding transfers
before shutting down. If CPUAnalyse is asserted then all inputs continue but outputs will not make
another access to memory for data. Memory refresh will continue to take place.
11.2 Bootstrap
The ST20-GP1 can be bootstrapped from external ROM, internal ROM or from a link. This is
determined by the setting of the BootSource0-1 pins, see Table 9.1 on page 52. If both
BootSource0-1 pins are held low it will boot from a link. If either or both pins are held high, it will
boot from ROM. This is sampled once only by the ST20-GP1, before the first instruction is
executed after reset.
11.2.1 Booting from ROM
When booting from ROM, the ST20-GP1 starts to execute code from the top two bytes in external
memory, at address #7FFFFFFE which should contain a backward jump to a program in ROM.
11.2.2 Booting from link
When booting from a link, the ST20-GP1 will wait for the first bootstrap message to arrive on the
link. The first byte received down the link is the control byte. If the control byte is greater than 1 (i.e.
2 to 255), it is taken as the length in bytes of the boot code to be loaded down the link. The bytes
following the control byte are then placed in internal memory starting at location MemStart.
Following reception of the last byte the ST20-GP1 will start executing code at MemStart. The
memory space immediately above the loaded code is used as work space. A byte arriving on the
bootstrapping link after the last bootstrap byte, is retained and no acknowledge is sent until a
process inputs from the link.
11.2.3 Peek and poke
Any location in internal or external memory can be interrogated and altered when the ST20-GP1 is
waiting for a bootstrap from link.
When booting from link, if the first byte (the control byte) received down the link is greater than 1, it
is taken as the length in bytes of the boot code to be loaded down the link.
If the control byte is 0 then eight more bytes are expected on the link. The first four byte word is
taken as an internal or external memory address at which to poke (write) the second four byte
word.
If the control byte is 1 the next four bytes are used as the address from which to peek (read) a word
of data; the word is sent down the output channel of the link.
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Control byte
Poke
0
1
address
address
data
data
Peek
reply
1
n
Bootstrap
n
bootstrap
where n is 2 to 255
Figure 11.1 Peek, poke and bootstrap
Note, peeks and pokes in the address range #20000000 to #3FFFFFFF access the internal
peripheral device registers. Therefore they can be used to configure the EMI before booting. Note
that addresses that overlap the internal peripheral addresses (#20000000 to 3FFFFFFF) can not
be accessed via the link.
Following a peek or poke, the ST20-GP1 returns to its previously held state. Any number of
accesses may be made in this way until the control byte is greater than 1, when the ST20-GP1 will
commence reading its bootstrap program.
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ST20-GP1
12 Serial link interface (OS-Link)
The OS-Link based serial communications subsystem provides serial data transfer. Its main
function is for booting the device during software development.
The OS-Link is a serial communications engine consisting of two signal wires, one in each
direction. OS-Links use an asynchronous bit-serial (byte-stream) protocol, each bit received is
sampled five times, hence the term over-sampled links (OS-Links). The OS-Link provides a pair of
channels, one input and one output channel.
The OS-Link is used for the following purposes:
•
Bootstrapping — the program which is executed at power up or after reset can reside in
ROM in the address space, or can be loaded via the OS-Link directly into memory.
•
Diagnostics — diagnostic and debug software can be downloaded over the link connected
to a PC or other diagnostic equipment, and the system performance and functionality can
be monitored.
•
Communicating with OS-Link peripherals or other ST20 devices.
12.1 OS-Link protocol
The quiescent state of a link output is low. Each data byte is transmitted as a high start bit followed
by a one bit followed by eight data bits followed by a low stop bit (see Figure 12.1). The least
significant bit of data is transmitted first. After transmitting a data byte the sender waits for the
acknowledge, which consists of a high start bit followed by a zero bit. The acknowledge signifies
both that a process was able to receive the acknowledged data byte and that the receiving link is
able to receive another byte. The sending link reschedules the sending process only after the
acknowledge for the final byte of the message has been received. The link allows an acknowledge
to be sent before the data has been fully received.
H
H
0
1
2
3
4
5
6
7
L
H
L
Ack
Data
Figure 12.1 OS-Link data and acknowledge formats
12.2 OS-Link speed
The OS-Link data rate is 19.6416 Mbits/s. This rate is the result of basing the clock on the
GPS-specific 16.368 MHz input. Standard 20 MHz development systems are not within
specification, but operate correctly under benign conditions. To operate within spec, the reference
clock for 5 MHz (B008, C011, C012) systems should be changed to 4.9104 MHz, for 10 MHz to
9.8208 MHz.
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ST20-GP1
12.3 OS-Link connections
Links are TTL compatible and intended to be used in electrically quiet environments, between
devices on a single printed circuit board or between two boards via a backplane. Direct connection
may be made between devices separated by a distance of less than 300 mm. For longer distances
a matched 100 ohm transmission line should be used with series matching resistors (RM), see
Figure 12.3. When this is done the line delay should be less than 0.4 bit time to ensure that the
reflection returns before the next data bit is sent. Buffers may be used for very long transmissions,
see Figure 12.4. If so, their overall propagation delay should be stable within the skew tolerance of
the link, although the absolute value of the delay is immaterial.
OSLinkOut
OSLinkIn
OSLinkIn
OSLinkOut
Figure 12.2 OS-Links directly connected
OSLinkOut
OSLinkIn
OSLinkIn
RM
Zo=100 ohms
OSLinkOut
RM
Zo=100 ohms
Figure 12.3 OS-Links connected by transmission line
OSLinkOut
OSLinkIn
OSLinkIn
buffers
OSLinkOut
Figure 12.4 OS-Links connected by buffers
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ST20-GP1
13 UART interface (ASC)
The UART interface, also referred to as the Asynchronous Serial Controller (ASC), provides serial
communication between the ST20 device and other microcontrollers, microprocessors or external
peripherals.
The ASC supports full-duplex asynchronous communication, where both the transmitter and the
receiver use the same data frame format and the same baud rate. Data is transmitted on the
transmit data output pin (TXD) and received on the receive data input pin (RXD).
Reload register
CPU
Baud rate timer
clock
Run
4 -input OR
gate
StopBits
Mode
ASC_interrupt
Receive buffer
full interrupt
Clock
RxEnable
ParityOdd
Transmitter
empty interrupt
Serial port control
Shift clock
Transmit buffer
empty interrupt
LoopBack
Error
interrupt
RXD
0
Receive shift
Transmit shift
register
MUX
1
Sampling
TXD
register
Receive buffer
register (RxBuffer)
Transmit buffer
register (TxBuffer)
Internal bus
Figure 13.1 Block diagram of the ASC
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ST20-GP1
Eight or nine bit data transfer, parity generation, and the number of stop bits are programmable.
Parity, framing, and overrun error detection is provided to increase the reliability of data transfers.
Transmission and reception of data is double-buffered. For multiprocessor communication, a
mechanism to distinguish address from data bytes is included. Testing is supported by a loop-back
option. A 16-bit baud rate generator provides the ASC with a separate serial clock signal.
13.1 Asynchronous serial controller operation
The operating mode of the serial channel ASC is controlled by the control register (ASCControl).
This register contains control bits for mode and error check selection, and status flags for error
identification.
A transmission is started by writing to the transmit buffer register (ASCTxBuffer), see Table 13.3.
Data transmission is double-buffered, therefore a new character may be written to the transmit
buffer register, before the transmission of the previous character is complete. This allows
characters to be sent back-to-back without gaps.
Data reception is enabled by the receiver enable bit (RxEnable) in the ASCControl register. After
reception of a character has been completed the received data, and received parity bit if selected,
can be read from the receive buffer register (ASCRxBuffer), refer to Table 13.4.
Data reception is double-buffered, so the reception of a second character may begin before the
previously received character has been read out of the receive buffer register. The overrun error
status flag (OverrunError) in the status register (ASCStatus), see Table 13.7, will be set when the
receive buffer register has not been read by the time reception of a second character is complete.
The previously received character in the receive buffer is overwritten, and the ASCStatus register
is updated to reflect the reception of the new character.
The loop-back option (selected by the LoopBack bit) internally connects the output of the
transmitter shift register to the input of the receiver shift register. This may be used to test serial
communication routines at an early stage without having to provide an external network.
13.1.1 Data frames
Data frames are selected by the setting of the Mode bit field in the ASCControl register, see Table
13.5.
8-bit data frames
8-bit data frames consist of:
•
•
eight data bits D0-7;
seven data bits D0-6 plus an automatically generated parity bit.
Parity may be odd or even, depending on the ParityOdd bit in the ASCControl register. An even
parity bit will be set, if the modulo-2-sum of the seven data bits is 1. An odd parity bit will be cleared
in this case. The parity error flag (ParityError) will be set if a wrong parity bit is received. The parity
bit itself will be stored in bit 7 of the ASCRxBuffer register.
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ST20-GP1
start
bit (LSB)
D0
D1
D2
D3
D4
D5
D6
8th
bit
1st
stop stop
bit bit
2nd
• Data bit (D7)
• Parity bit
Figure 13.2 8-bit data frames
9-bit data frames
9-bit data frames consist of:
•
•
•
nine data bits D0-8;
eight data bits D0-7 plus an automatically generated parity bit;
eight data bits D0-7 plus a wake-up bit.
Parity may be odd or even, depending on the ParityOdd bit in the ASCControl register. An even
parity bit will be set, if the modulo-2-sum of the eight data bits is 1. An odd parity bit will be cleared
in this case. The parity error flag (ParityError) will be set if a wrong parity bit is received. The parity
bit itself will be stored in bit 8 of the ASCRxBuffer register, see Table 13.4.
In wake-up mode, received frames are only transferred to the receive buffer register if the ninth bit
(the wake-up bit) is 1. If this bit is 0, no receive interrupt request will be activated and no data will
be transferred. This feature can be used to control communication in multi-processor systems.
When the master processor wants to transmit a block of data to one of several slaves, it first sends
out an address byte which identifies the target slave. An address byte differs from a data byte in
that the additional ninth bit is a 1 for an address byte and a 0 for a data byte, so no slave will be
interrupted by a data byte. An address byte will interrupt all slaves (operating in 8-bit data + wake-
up bit mode), so each slave can examine the 8 least significant bits (LSBs) of the received
character (the address). The addressed slave will switch to 9-bit data mode, which enables it to
receive the data bytes that will be coming (with the wake-up bit cleared). The slaves that are not
being addressed remain in 8-bit data + wake-up bit mode, ignoring the following data bytes.
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ST20-GP1
2nd
stop
bit
1st
stop
bit
start
bit
D0
(LSB)
D1
D2
D3
D4
D5
D6
D7
9th
bit
• Data bit (D8)
• Parity bit
• Wake-up bit
Figure 13.3 9-bit data frames
Transmission
Transmission begins at the next overflow of the divide-by-16 counter (see Figure 13.3 above),
provided that the Run bit is set and data has been loaded into the ASCTxBuffer. The transmitted
data frame consists of three basic elements:
•
•
•
the start bit
the data field (8 or 9 bits, least significant bit (LSB) first, including a parity bit, if selected)
the stop bits (0.5, 1, 1.5 or 2 stop bits)
Data transmission is double buffered. When the transmitter is idle, the transmit data written into the
transmit buffer is immediately moved to the transmit shift register, thus freeing the transmit buffer
for the next data to be sent. This is indicated by the transmit buffer empty flag (TxBufEmpty) being
set. The transmit buffer can be loaded with the next data, while transmission of the previous data is
still going on.
The transmitter empty flag (TxEmpty) will be set at the beginning of the last data frame bit that is
transmitted, i.e. during the first system clock cycle of the first stop bit shifted out of the transmit shift
register.
Reception
Reception is initiated by a falling edge on the data input pin (RXD), provided that the Run and
RxEnable bits are set. The RXD pin is sampled at 16 times the rate of the selected baud rate. A
majority decision of the first, second and third samples of the start bit determines the effective bit
value. This avoids erroneous results that may be caused by noise.
If the detected value is not a 0 when the start bit is sampled, the receive circuit is reset and waits
for the next falling edge transition of the RXD pin. If the start bit is valid, the receive circuit
continues sampling and shifts the incoming data frame into the receive shift register. For
subsequent data and parity bits, the majority decision of the seventh, eighth and ninth samples in
each bit time is used to determine the effective bit value.
For 0.5 stop bits, the majority decision of the third, fourth, and fifth samples during the stop bit is
used to determine the effective stop bit value.
For 1 and 2 stop bits, the majority decision of the seventh, eighth, and ninth samples during the
stop bits is used to determine the effective stop bit values.
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ST20-GP1
For 1.5 stop bits, the majority decision of the fifteenth, sixteenth, and seventeenth samples during
the stop bits is used to determine the effective stop bit value.
When the last stop bit has been received (at the end of the last programmed stop bit period) the
content of the receive shift register is transferred to the receive data buffer register
(ASCRxBuffer). The receive buffer full flag (RxBufFull) is set, and the parity (ParityError) and
framing error (FrameError) flags are updated, after the last stop bit has been received (at the end
of the last stop bit programmed period), regardless of whether valid stop bits have been received or
not. The receive circuit then waits for the next start bit (falling edge transition) at the RXD pin.
Reception is stopped by clearing the RxEnable bit. A currently received frame is completed
including the generation of the receive status flags. Start bits that follow this frame will not be
recognized.
Note: In wake-up mode, received frames are only transferred to the receive buffer register if the ninth
bit (the wake-up bit) is 1. If this bit is 0, the receive buffer full (RxBufFull) flag will not be set and no
data will be transferred.
13.2 Hardware error detection capabilities
To improve the safety of serial data exchange, the ASC provides three error status flags in the
ASCStatus register which indicate if an error has been detected during reception of the last data
frame and associated stop bits.
The parity error (ParityError) bit is set when the parity check on the received data is incorrect.
The framing error (FrameError) bit is set when the RXD pin is not a 1 during the programmed
number of stop bit times, sampled as described in the section above.
The overrun error (OverrunError) bit is set when the last character received in the ASCRxBuffer
register has not been read out before reception of a new frame is complete.
These flags are updated simultaneously with the transfer of data to the receive buffer.
13.3 Baud rate generation
The ASC has its own dedicated 16-bit baud rate generator with 16-bit reload capability.
The baud rate generator is clocked with the CPU clock. The timer counts downwards and can be
started or stopped by the Run bit in the ASCControl register. Each underflow of the timer provides
one clock pulse. The timer is reloaded with the value stored in its 16-bit reload register each time it
underflows. The ASCBaudRate register is the dual-function baud rate generator/reload register. A
read from this register returns the content of the timer, writing to it updates the reload register.
An auto-reload of the timer with the content of the reload register is performed each time the
ASCBaudRate register is written to. However, if the Run bit is 0 at the time the write operation to
the ASCBaudRate register is performed, the timer will not be reloaded until the first CPU clock
cycle after the Run bit is 1.
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ST20-GP1
13.3.1 Baud rates
The baud rate generator provides a clock at 16 times the baud rate. The baud rate and the required
reload value for a given baud rate can be determined by the following formulas:
f
CPU
Baud rate =
16 (<ASCBaudRate>)
f
CPU
<ASCBaudRate> = (
)
16 x Baud rate
where: <ASCBaudRate> represents the content of the ASCBaudRate register, taken as unsigned
16-bit integer,
f
is the frequency of the CPU.
CPU
Note that altering the CPU speed selection pins will thus change the baud rate. Software can
accommodate this by reading the SysRatio register, see section 10.3, in calculating the CPU
frequency.
The table below lists various commonly used baud rates together with the required reload values
and the deviation errors for the ST20-GP1 using a CPU clock of 33.736 MHz.
Baud rate
Reload value
(exact)
Reload value
(integer)
Reload value
(hex)
Deviation error
38400
28800
19200
14400
9600
4800
2400
1200
600
53.28125
71.04167
106.5625
142.0833
213.125
426.25
852.5
53
35
-0.53%
-0.06%
0.41%
-0.06%
-0.06%
-0.06%
0.06%
0.00%
0.00%
0.00%
0.00%
71
47
107
142
213
426
853
1705
3410
6820
27280
6B
8E
D5
1AA
355
6A9
D52
1AA4
6A90
1705
3410
300
6820
75
27280
Table 13.1 Baud rates
Note: The deviation errors given in the table above are rounded.
13.4 Interrupt control
The ASC contains two registers that are used to control interrupts, the status register (ASCStatus)
and the interrupt enable register (ASCIntEnable). The status bits in the ASCStatus register
determine the cause of the interrupt. Interrupts will occur when a status bit is 1 (high) and the
corresponding bit in the ASCIntEnable register is 1.
The error interrupt signal (ErrorInterrupt) is generated by the ASC from the OR of the parity error,
framing error, and overrun error status bits after they have been ANDed with the corresponding
enable bits in the ASCIntEnable register.
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ST20-GP1
An overall interrupt request signal (ASC_interrupt) is generated from the OR of the ErrorInterrupt
signal and the TxEmpty, TxBufEmpty and RxBufFull signals.
Note: the status register cannot be written directly by software. The reset mechanism for the status
register is described below.
The transmitter interrupt status bits (TxEmpty, TxBufEmpty) are reset when a character is written
to the transmitter buffer.
The receiver interrupt status bit (RxBufFull) is reset when a character is read from the receive
buffer.
The error status bits (ParityError, FrameError, OverrunError) are reset when a character is read
from the receive buffer.
Receive buffer
full interrupt
&
&
&
&
&
&
RxBufFull
TxEmpty
RxBufFullIE
TxEmptyIE
Transmitter
empty interrupt
Transmit buffer
empty interrupt
TxBufEmpty
ParityError
FrameError
TxBufEmptyIE
ParityErrorIE
FrameErrorIE
OverrunError
OverrunErrorIE
OR
RESERVED
read 0, write 0
RESERVED
read 0, write 0
Error interrupt
ASCStatus
register
ASCIntEnable
register
Figure 13.4 ASC status and interrupt registers
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ST20-GP1
13.4.1 Using the ASC interrupts
For normal operation (i.e. besides the error interrupt) the ASC provides three interrupt requests to
control data exchange via the serial channel:
•
TxBufEmpty is activated when data is moved from ASCTxBuffer to the transmit shift reg-
ister.
•
•
TxEmpty is activated before the last bit of a frame is transmitted.
RxBufFull is activated when the received frame is moved to ASCRxBuffer.
The transmitter generates two interrupts. This provides advantages for the servicing software.
For single transfers it is sufficient to use the transmitter interrupt (TxEmpty), which indicates that
the previously loaded data has been transmitted, except for the last bit of a frame.
For multiple back-to-back transfers it is necessary to load the next data before the last bit of the
previous frame has been transmitted. This leaves just one bit-time for the handler to respond to the
transmitter interrupt request.
Using the transmit buffer interrupt (TxBufEmpty) to reload transmit data allows the time to transmit
a complete frame for the service routine, as ASCTxBuffer may be reloaded while the previous
data is still being transmitted.
As shown in Figure 13.5 below, TxBufEmpty is an early trigger for the reload routine, while
TxEmpty indicates the completed transmission of the data field of the frame. Therefore, software
using handshake should rely on TxEmpty at the end of a data block to make sure that all data has
really been transmitted.
TxEmpty
TxBufEmpty
TxEmpty
TxBufEmpty
TxEmpty
TxBufEmpty
Idle
Idle
RxBufFull
RxBufFull
RxBufFull
Figure 13.5 ASC interrupt generation
13.5 ASC configuration registers
ASCBaudRate register
The ASCBaudRate register is the dual-function baud rate generator/reload register.
A read from this register returns the content of the timer, writing to it updates the reload register.
An auto-reload of the timer with the content of the reload register is performed each time the
ASCBaudRate register is written to. However, if the Run bit of the ASCControl register, see Table
13.5, is 0 at the time the write operation to the ASCBaudRate register is performed, the timer will
not be reloaded until the first CPU clock cycle after the Run bit is 1.
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ST20-GP1
ASCBaudRate
ASC base address + #00
Write Function
Read/Write
Bit
Bit field
ReloadVal
Read Function
15:0
16-bit reload value
16-bit count value
Table 13.2 ASCBaudRate register format
ASCTxBuffer register
Writing to the transmit buffer register starts data transmission.
ASCTxBuffer
ASC base address + #04
Function
Write only
Bit
0
Bit field
TD0
TD1
TD2
TD3
TD4
TD5
TD6
Transmit buffer data D0
Transmit buffer data D1
Transmit buffer data D2
Transmit buffer data D3
Transmit buffer data D4
Transmit buffer data D5
Transmit buffer data D6
1
2
3
4
5
6
7
TD7/Parity Transmit buffer data D7, or parity bit - dependent on the operating mode (the setting of the
Mode field in the ASCControl register).
8
TD8/Parity Transmit buffer data D8, or parity bit, or wake-up bit or undefined - dependent on the operating
/Wake/0
mode (the setting of the Mode field in the ASCControl register).
Note: If the Mode field selects an 8-bit frame then this bit should be written as 0.
15:9
RESERVED. Write 0.
Table 13.3 ASCTxBuffer register format
ASCRxBuffer register
The received data and, if provided by the selected operating mode, the received parity bit can be
read from the receive buffer register.
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ST20-GP1
ASCRxBuffer
ASC base address + #08
Function
Read only
Bit
0
Bit field
RD0
RD1
RD2
RD3
RD4
RD5
RD6
Receive buffer data D0
Receive buffer data D1
Receive buffer data D2
Receive buffer data D3
Receive buffer data D4
Receive buffer data D5
Receive buffer data D6
1
2
3
4
5
6
7
RD7/Parity Receive buffer data D7, or parity bit - dependent on the operating mode (the setting of the
Mode bit in the ASCControl register).
Note: If the Mode field selects a 7-bit frame then this bit is undefined. Software should ignore
this bit when reading 7-bit frames.
8
RD8/Parity/ Receive buffer data D8, or parity bit, or wake-up bit - dependent on the operating mode (the
Wake/X
setting of the Mode field in the ASCControl register).
Note: If the Mode field selects a 7- or 8-bit frame then this bit is undefined. Software should
ignore this bit when reading 7- or 8-bit frames.
15:9
RESERVED. Will read back 0.
Table 13.4 ASCRxBuffer register format
ASCControl register
This register controls the operating mode of the ASC and contains control bits for mode and error
check selection, and status flags for error identification.
Note: Programming the mode control field (Mode) to one of the reserved combinations may result
in unpredictable behavior.
Note: Serial data transmission or reception is only possible when the baud rate generator run bit
(Run) is set to 1. When the Run bit is set to 0, TXD will be 1. Setting the Run bit to 0 will
immediately freeze the state of the transmitter and receiver. This should only be done when the
ASC is idle.
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ST20-GP1
ASCControl
ASC base address + #0C
Function
Read/Write
Bit
Bit field
2:0
Mode
ASC mode control
Mode2:0
000
001
Mode
RESERVED
8-bit data
010
011
100
RESERVED
7-bit data + parity
9-bit data
101
110
111
8-bit data + wake up bit
RESERVED
8-bit data + parity
4:3
StopBits
Number of stop bits selection
StopBits1:0
Number of stop bits
00
01
10
11
0.5 stop bits
1 stop bit
1.5 stop bits
2 stop bits
5
ParityOdd
LoopBack
Run
Parity selection
0
1
Even parity (parity bit set on odd number of ‘1’s in data)
Odd parity (parity bit set on even number of ‘1’s in data)
6
Loopback mode enable bit
0
1
Standard transmit/receive mode
Loopback mode enabled
7
Baud rate generator run bit
0
1
Baud rate generator disabled (ASC inactive)
Baud rate generator enabled
8
RxEnable
Receiver enable bit
0
1
Receiver disabled
Receiver enabled
15:9
RESERVED. Write 0, will read back 0.
Table 13.5 ASCControl register format
ASCIntEnable register
The ASCIntEnable register enables a source of interrupt.
Interrupts will occur when a status bit in the ASCStatus register is 1, and the corresponding bit in
the ASCIntEnable register is 1.
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ST20-GP1
ASCIntEnable
ASC base address + #10
Function
Read/Write
Bit
Bit field
0
RxBufFullIE
Receiver buffer full interrupt enable
0
1
receiver buffer full interrupt disable
receiver buffer full interrupt enable
1
TxEmptyIE
Transmitter empty interrupt enable
0
1
transmitter empty interrupt disable
transmitter empty interrupt enable
2
TxBufEmptyIE
ParityErrorIE
FrameErrorIE
OverrunErrorIE
Transmitter buffer empty interrupt enable
0
1
transmitter buffer empty interrupt disable
transmitter buffer empty interrupt enable
3
Parity error interrupt enable
0
1
parity error interrupt disable
parity error interrupt enable
4
Framing error interrupt enable
0
1
framing error interrupt disable
framing error interrupt enable
5
Overrun error interrupt enable
0
1
overrun error interrupt disable
overrun error interrupt enable
7:6
RESERVED. Write 0, will read back 0.
Table 13.6 ASCIntEnable register format
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ST20-GP1
ASCStatus register
The ASCStatus register determines the cause of an interrupt.
ASCStatus
ASC base address + #14
Function
Read Only
Bit
Bit field
0
RxBufFull
Receiver buffer full flag
0
1
receiver buffer not full
receiver buffer full
1
TxEmpty
Transmitter empty flag
0
1
transmitter not empty
transmitter empty
2
TxBufEmpty
ParityError
FrameError
OverrunError
Transmitter buffer empty flag
0
1
transmitter buffer not empty
transmitter buffer empty
3
Parity error flag
0
1
no parity error
parity error
4
Framing error flag
0
1
no framing error
framing error
5
Overrun error flag
0
1
no overrun error
overrun error
7:6
RESERVED. Write 0, will read back 0.
Table 13.7 ASCStatus register format
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ST20-GP1
14 Parallel input/output
The ST20-GP1 device has 6 bits of Parallel Input/Output (PIO), each bit is programmable as an
input or an output.
The input bits can be compared against a register and an interrupt generated when the value is not
equal.
14.1 PIO Port
Each of the bits of the PIO port has a corresponding bit in the PIO registers associated with the
port. These registers hold: output data for the port (POut); the input data read from the pin (PIn);
PIO bit configuration register (PC1); and the two input compare function registers (PComp and
PMask).
All of the registers, except the PIn register, are each mapped onto three separate addresses so
that bits can be set or cleared individually.
The Set_ register allows bits to be set individually. Writing a ‘1’ in this register sets the
corresponding bit in the associated register, a ‘0’ leaves the bit unchanged.
The Clear_ register allows bits to be cleared individually. Writing a ‘1’ in this register resets the
corresponding bit in the associated register, a ‘0’ leaves the bit unchanged.
14.1.1 PIO Data registers
The base addresses for the PIO registers are given in the Memory Map chapter.
POut register
This register holds output data for the port.
POut
PIO port base address + #00
Function
Read/Write
Bit
0
Bit field
POut0
POut1
POut2
POut3
POut4
POut5
Output data bit 0
Output data bit 1
Output data bit 2
Output data bit 3
Output data bit 4
Output data bit 5
1
2
3
4
5
Table 14.1 POut register format
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ST20-GP1
PIn register
The data read from this register will give the logic level present on an input pin at the start of the
read cycle to this register. The read data will be the last value written to the register irrespective of
the pin configuration selected.
PIn
Bit
0
PIO port base address + #10
Function
Read only
Bit field
PIn0
Input data bit 0
Input data bit 1
Input data bit 2
Input data bit 3
Input data bit 4
Input data bit 5
1
PIn1
2
PIn2
3
PIn3
4
PIn4
5
PIn5
Table 14.2 PIn register format
14.1.2 PIO bit configuration register
The PC1 register is used to configure each of the PIO port bits as an input or output. Writing a 0
configures the bit as an input, a 1 configures the bit as an output.
PC1
Bit
0
PIO port base address + #30
Function
Read/Write
Bit field
ConfigData0
ConfigData1
ConfigData2
ConfigData3
ConfigData4
ConfigData5
Configures the PIO bit 0 as an input or an output.
1
Configures the PIO bit 1 as an input or an output.
Configures the PIO bit 2 as an input or an output.
Configures the PIO bit 3 as an input or an output.
Configures the PIO bit 4 as an input or an output.
Configures the PIO bit 5 as an input or an output.
2
3
4
5
Table 14.3 PC1 register format
14.1.3 PIO Input compare and Compare mask registers
The input compare (PComp) register holds the value to which the input data from the PIO port pins
will be compared. If any of the input bits are different from the corresponding bits in the PComp
register, and the corresponding bit in the compare mask (PMask) register is set to 1, then the
internal interrupt signal for the port will be set to 1.
The compare function is sensitive to changes in levels on the pins and so the change in state on
the input pin must be greater in duration than the interrupt response time for the compare to be
seen as a valid interrupt by an interrupt service routine.
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ST20-GP1
PComp
PIO port base address + #50
Function
Read/Write
Bit
0
Bit field
PComp0
PComp1
PComp2
PComp3
PComp4
PComp5
Value to which input data bit 0 will be compared.
1
Value to which input data bit 1 will be compared.
Value to which input data bit 2 will be compared.
Value to which input data bit 3 will be compared.
Value to which input data bit 4 will be compared.
Value to which input data bit 5 will be compared.
2
3
4
5
Table 14.4 PComp register format
PMask
Bit
PIO port base address + #60
Function
Read/Write
Bit field
PMask0
0
When set to 1, the compare function for the internal interrupt for the port is enabled.
When enabled, if input data bit 0 is different to PComp0 then an interrupt is generated.
1
2
3
4
5
PMask1
PMask2
PMask3
PMask4
PMask5
When set to 1, the compare function for the internal interrupt for the port is enabled.
When enabled, if input data bit 1 is different to PComp1 then an interrupt is generated.
When set to 1, the compare function for the internal interrupt for the port is enabled.
When enabled, if input data bit 2 is different to PComp2 then an interrupt is generated.
When set to 1, the compare function for the internal interrupt for the port is enabled.
When enabled, if input data bit 3 is different to PComp3 then an interrupt is generated.
When set to 1, the compare function for the internal interrupt for the port is enabled.
When enabled, if input data bit 4 is different to PComp4 then an interrupt is generated.
When set to 1, the compare function for the internal interrupt for the port is enabled.
When enabled, if input data bit 5 is different to PComp5 then an interrupt is generated.
Table 14.5 PMask register format
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ST20-GP1
15 Byte-wide parallel port
The byte-wide parallel port is provided to drive an external device using 8-bit half-duplex streamed
I/O and two control wires.
The byte-wide parallel port has 2 modes of operation, as follows:
•
it can operate as an ASIC interface. In this mode the external data transfer is controlled by
the EMI strobes and addresses.
•
it can operate as a byte-wide parallel link (PLink) using an external asynchronous transfer
mechanism to control transfers.
The mode of operation is determined by the setting of the configuration registers, see Section 15.3.
15.1 EMI mode operation
In this mode the EMI is in total control of the PlinkData0-7 pins. The PlinknotAck output is forced
to its ‘inactive’ state during this mode.
The interface to the external device is controlled by the EMI. The bottom 8 bits of the EMI data bus
(MemData0-7) are redirected (copied) to the PlinkData0-7 pins. The direction of these pads is
controlled by the EMI. The external timing and data transfer of this activity is controlled by the
programmed configuration of the EMI bank 2 (see Section 9.5 on page 58).
15.2 Parallel link (DMA) mode operation
In this mode the byte-wide parallel port is a DMA (direct memory access) engine which performs
memory transfers to and from the external links on behalf of a controller (the CPU). The parallel link
is unidirectional and only transfers data in one direction across the memory bus at any given time.
The byte-wide parallel port defaults to input (to the ST20-GP1) when the ST20-GP1 is reset (with
the notRST pin) to prevent contention, and can be used for DMA functions without interfering with
memory bank 2. However to access external registers via the PlinkData0-7 pins, the bit in the
PlinkEmi register (see Table 15.1) must be set by software. This results in all accesses to external
memory bank 2 being diverted via the port rather than MemData0-7, allowing both register and
DMA access to the external peripheral. External memory bank 2 must be dedicated solely for this
use while the register access of this external peripheral is enabled.
Being half-duplex, the direction of the link when in DMA mode must be selected in software by
setting the bit in the PlinkIO register (see Table 15.2 below). Data transfer for the parallel port (for
DMA transfers) occur by the use of a channel. When the EMI is using these pads the directionality
is controlled by the EMI and not the DMA control register.
15.3 Configuration registers
There are three control registers for the parallel port which are programmed by use of devsw
(device store) and devlw (device load) instructions. The base address for the parallel port
configuration registers is given in the Memory Map chapter.
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ST20-GP1
PlinkEmi register
The PlinkEmi register determines the mode of operation of the port.
PlinkEmi
Parallel port base address + #00
Read/Write
Bit
Bit field
Function
This bit determines the mode of operation of the port.
0
PlinkEmi
PlinkEmi
Mode
0
1
DMA mode (reset state)
EMI mode
Table 15.1 PlinkEmi register format
PlinkIO
The PlinkIO register determines the direction of the port interactions when in the DMA mode of
operation.
PlinkIO
Parallel port base address + #04
Function
Read/Write
Bit
Bit field
PlinkIO
This bit controls the direction of the parallel port interactions when in DMA mode.
0
PlinkIO
Direction
0
1
inputs (reset state)
outputs
Table 15.2 PlinkIO register format
PlinkMode
The PlinkMode register determines the external protocol used for interactions.
PlinkMode
Parallel port base address + #08
Read/Write
Bit
Bit field
PlinkMode
Function
These bits control the external protocol used for interactions.
0
PlinkMode
Protocol
00
01
10
11
Idle (reset state)
Dreq/Dack mode
Valid/Ack mode
Direct mode
Table 15.3 PlinkMode register format
15.4 External data transfer protocols
The byte-wide parallel port has three control pins. PlinknotReq and PlinknotAck control data
transfers and the PlinkOut pin controls external buffers, if required (e.g. an external 3V/5V buffer
device). When the PlinkOut pin is high it signals the plink is outputting.
The control pins can support three external protocols, as follows:
•
•
•
Dreq/Dack protocol
Valid/Ack protocol
Direct DMA protocol
The protocol used for interactions is programmable via the PlinkMode register. In addition, the
direction of the link is controlled by the PlinkIO register (see Table 15.2).
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ST20-GP1
15.4.1 Dreq/Dack protocol
In this mode the 2 control pins PlinknotReq (Dreq) and PlinknotAck (Dack) are active low. The
initial (inactive) state of the 2 control wires is high.
Dreq/Dack output
The sequence of events for a Dreq/Dack output is outlined below.
1 PlinknotReq (Dreq), input to ST20, is taken low by the external ASIC.
2 The ST20-GP1 asserts the PlinknotAck (Dack) output low. The ASIC can then take
PlinknotReq (Dreq) high.
3 Following PlinknotAck (Dack) going low, the data in the DMA buffer is applied to the output
pins. PlinknotAck (Dack) is forced high and the output drivers are tristated. The ASIC can
initiate the next transfer.
Dreq/Dack input
The sequence of events for a Dreq/Dack input is outlined below.
1 PlinknotReq (Dreq), input to ST20, is taken low by the external ASIC.
2 The ST20-GP1 then asserts the PlinknotAck (Dack) output low.
3 The external ASIC applies the data to be transferred to the PlinkData0-7 pins. The ASIC
can then return PlinknotReq (Dreq) high at any time.
4 The data on the input pins is sampled, then PlinknotAck (Dack) is forced high.
ST20 Output
PlinknotReq
(Dreq)
PlinknotAck
(Dack)
PlinkData0-7
ST20 Input
PlinknotReq
(Dreq)
PlinknotAck
(Dack)
PlinkData0-7
Figure 15.1 Dreq/Dack protocol
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ST20-GP1
15.4.2 Valid/Ack protocol
In this mode the 2 control pins PlinknotReq (Qack/Ivalid) and PlinknotAck (Qvalid/Iack) are active
high. The initial (inactive) state of the 2 control wires is low.
Valid Ack output
An output transaction proceeds as follows.
1 The DMA is programmed to perform an out and the DMA engine receives its first byte in the
buffer from the EMI.
2 The PLink drives the data to the PlinkData0-7 pins and drives PlinknotAck (Qvalid) high.
3 The external device acknowledges receipt of the data by taking PlinknotReq (Qack) high.
The PLink can then take PlinknotAck (Qvalid) low.
4 The external device can take PlinknotReq (Qack) low ready for the next transaction.
Valid Ack input
An input transaction proceeds as follows.
1 The external device drives the data pins and PlinknotReq (Ivalid) is asserted high.
2 If the DMA engine has empty buffer space PlinkData0-7 is latched and PlinknotAck (Iack)
is driven high by the PLink. The DMA writes to the appropriate address in memory.
3 The external device can then drive PlinknotReq (Ivalid) low.
4 PlinknotAck (Iack) can be taken low. The external device can then initiate the next transac-
tion.
ST20 Output
PlinknotAck
(Qvalid)
PlinknotReq
(Qack)
old data
valid data
PlinkData0-7
ST20 Input
PlinknotReq
(Ivalid)
PlinknotAck
(Iack)
PlinkData0-7
Figure 15.2 Valid/Ack protocol
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ST20-GP1
15.4.3 Direct DMA protocol
In this mode the PLink becomes an unsynchronized (i.e. direct action) bus. The PlinknotAck
output still behaves as if it were acknowledging a real transfer. The PlinknotReq signal has no
effect in this mode of operation. In this mode PlinknotAck is active high. The initial (inactive) state
of the pin is low.
Direct mode output
To drive the output pins the PLink must be programmed to make a single byte DMA. If more than
one byte is output, the PLink will continue to drive the output pins as fast as the output DMA can
feed the data, i.e. once every 8 or more system clock cycles, until the correct number of bytes have
been output. The sequence of events for a single byte read is outlined below. When configured as
an output the drivers are always driven.
1 The PLink forces the PlinknotAck pin high. The output pins are then driven with the new
data and the PlinknotAck pin is forced low.
2 The output data remains static and driven to the pads until either a new value is written as
output or until the link direction is changed. If the PLink returns to direct output mode, the
old data is once again driven to the pads.
Note: At reset PlinknotAck is a logic one, appearing to the outside world as an ‘acknowledge’.
External logic will assume that the data has been read. Therefore after programming the PLink to
direct mode the PlinknotAck output falls.
Direct mode input
To read the input pins the PLink must be programmed to make a single byte DMA. The sequence
of events for a single byte read is outlined below.
1 The PLink forces the PlinknotAck pin high. The input pins are then read and the Plinkno-
tAck pin is forced low.
ST20 Output
PlinknotAck
PlinkData0-7
valid data
ST20 Input
PlinknotAck
PlinkData0-7
Figure 15.3 Direct DMA protocol
92/116
ST20-GP1
16 Configuration register addresses
This chapter lists all the ST20-GP1 configuration registers and gives the addresses of the registers.
The complete bit format of each of the registers and its functionality is given in the relevant chapter.
The registers can be examined and set by the devlw (device load word) and devsw (device store
word) instructions. Note, they cannot be accessed using memory instructions.
Read/
Register
Address
Size
Set
Clear
Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
W
HandlerWptr0
HandlerWptr1
HandlerWptr2
HandlerWptr3
HandlerWptr4
TriggerMode0
TriggerMode1
TriggerMode2
TriggerMode3
TriggerMode4
Pending
#20000000
#20000004
#20000008
#2000000C
#20000010
#20000040
#20000044
#20000048
#2000004C
#20000050
#20000080
#20000084
#20000088
#200000C0
#200000C4
#200000C8
#20000100
#20000104
#20000108
#20000400
#20000404
#20000408
32
32
32
32
32
3
3
3
3
3
5
Interrupt trigger
Interrupt grant
Set_Pending
Clear_Pending
Mask
5
5
W
17
17
17
5
R/W
W
Set_Mask
Clear_Mask
Exec
W
Interrupt valid
Interrupt done
R/W
W
Set_Exec
5
Clear_Exec
LPTimerLS
LPTimerMS
LPTimerStart
5
W
32
32
1
R/W
R/W
By a write to LP- R/W
TimerLS or LP-
TimerMS
LPAlarmLS
LPAlarmMS
LPAlarmStart
LPSysPll
#20000410
#20000414
#20000418
#20000420
32
8
R/W
R/W
R/W
R/W
1
2
SysRatio
#20000500
#20000510
6
1
R
R/W
WdEnable
Table 16.1 ST20-GP1 configuration register addresses
93/116
ST20-GP1
Read/
Write
Register
Address
Size
Set
Clear
#20000514
#20002000
#20002004
#20002008
#2000200C
#20002010
#20002020
#20002030
#20004000
#20004004
#20004008
#2000400C
#20004010
#20004014
#20006000
#20006004
#20006008
#2000600C
#20006010
#20006014
#20008000
#20008004
#20008008
#20008010
#20008030
#20008034
#20008038
#20008050
#20008054
#20008058
#20008060
#20008064
#20008068
#2000A000
#2000A004
#2000A008
1
R
WdFlag
32
32
32
32
32
32
32
16
16
16
16
8
R/W
R/W
R/W
R/W
W
EmiConfigDataField0
EmiConfigDataField1
EmiConfigDataField2
EmiConfigDataField3
EmiConfigLock
EmiConfigStatus
EmiConfigStall
ASC0BaudRate
ASC0TxBuffer
ASC0RxBuffer
ASC0Control
ASC0IntEnable
ASC0Status
ASC1BaudRate
ASC1TxBuffer
ASC1RxBuffer
ASC1Control
ASC1IntEnable
ASC1Status
POut
R
W
R/W
W
R
R/W
R/W
R
8
16
16
16
16
8
R/W
W
R
R/W
R/W
R
8
6
R/W
W
6
Set_POut
6
W
Clear_POut
PIn
6
R
6
R/W
W
PC1
6
Set_PC1
6
W
Clear_PC1
6
R/W
W
PComp
6
Set_PComp
Clear_PComp
PMask
6
W
6
R/W
W
6
Set_PMask
6
W
Clear_PMask
PlinkEmi
1
R/W
R/W
R/W
1
PlinkIO
2
PlinkMode
Table 16.1 ST20-GP1 configuration register addresses
94/116
ST20-GP1
Read/
Write
Register
Address
Size
Set
Clear
#2000C000
#2000C004
#2000C008
#2000C00C
#2000C010
#2000C014
#2000C018
#2000C01C
#2000C020
#2000C024
#2000C028
#2000C02C
#2000C040
7
W
W
W
W
W
W
W
W
W
W
W
W
W
R
PRNcode0
7
PRNcode1
7
PRNcode2
7
PRNcode3
7
PRNcode4
7
PRNcode5
7
PRNcode6
7
PRNcode7
7
PRNcode8
7
PRNcode9
7
PRNcode10
7
PRNcode11
19
1
PRNphase0
PRNphase0WrEn
PRNphase1
#2000C044
#2000C048
#2000C04C
#2000C050
#2000C054
#2000C058
#2000C05C
#2000C060
#2000C064
#2000C068
#2000C06C
19
1
W
R
PRNphase1WrEn
PRNphase2
19
1
W
R
PRNphase2WrEn
PRNphase3
19
1
W
R
PRNphase3WrEn
PRNphase4
19
1
W
R
PRNphase4WrEn
PRNphase5
19
1
W
R
PRNphase5WrEn
PRNphase6
19
1
W
R
PRNphase6WrEn
PRNphase7
19
1
W
R
PRNphase7WrEn
PRNphase8
19
1
W
R
PRNphase8WrEn
PRNphase9
19
1
W
R
PRNphase9WrEn
PRNphase10
PRNphase10WrEn
PRNphase11
PRNphase11WrEn
19
1
W
R
19
1
W
R
Table 16.1 ST20-GP1 configuration register addresses
95/116
ST20-GP1
Read/
Write
Register
Address
Size
Set
Clear
#2000C080
#2000C084
#2000C088
#2000C08C
#2000C090
#2000C094
#2000C098
#2000C09C
#2000C0A0
#2000C0A4
#2000C0A8
#2000C0AC
#2000C0C0
#2000C0C4
#2000C0C8
#2000C0CC
#2000C0D0
#2000C0D4
#2000C0D8
#2000C0DC
#2000C0E0
#2000C0E4
#2000C0E8
#2000C0EC
#2000C100
#2000C104
#2000C140
18
18
18
18
18
18
18
18
18
18
18
18
7
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
NCOfrequency0
NCOfrequency1
NCOfrequency2
NCOfrequency3
NCOfrequency4
NCOfrequency5
NCOfrequency6
NCOfrequency7
NCOfrequency8
NCOfrequency9
NCOfrequency10
NCOfrequency11
NCOphase0
7
NCO1phase
7
NCOphase2
7
NCOphase3
7
NCOphase4
7
NCOphase5
7
NCOphase6
7
NCOphase7
7
NCOphase8
7
NCOphase9
7
NCOphase10
NCOphase11
PRNinitialVal0
PRNinitialVal1
DSPControl
7
10
10
4
Table 16.1 ST20-GP1 configuration register addresses
96/116
ST20-GP1
17 Electrical specifications
Absolute maximum ratings
Operation beyond the absolute maximum ratings may cause permanent damage to the device.
All voltages are measured referred to GND.
Symbol Parameter
Min
Max
Units Notes
VDD
VDDrtc
Ts
DC power supply
-0.5
-0.5
-55
-40
-20
-0.5
4.5
V
Voltage at RTCVDD pin referred to GND
Storage temperature (ambient)
4.5
V
125
°C
Tj
Temperature under bias (junction)
125
°C
mA
V
1
2
Io
Continuous DC output current from any output pin.
20
Vi
Applied voltage to all functional pins excluding LPClockIn,
notRST and test control pins.
VDD + 0.5
Virtc
Vo
Applied voltage to LPClockIn, notRST and test control pins.
-0.5
VDDrtc + 0.5
VDD + 0.5
VDDrtc + 0.5
2.0
V
Voltage on bi-directional and output pins except notMemCE0. -0.5
V
Vortc
PDmax
Voltage on the notMemCE0 pin
-0.5
V
Power dissipation in package
W
Table 17.1 Absolute maximum ratings
Notes
1 For a package junction to case thermal resistance of 14°C/W.
2 For reliability reasons the long-term current from any pin may be limited to a lower value
than stated here.
Operating conditions
Symbol
Parameter
Min
Max
Units
Notes
Ta
Tj
Ambient operating temperature of case
Operating temperature of junction
-40
-40
85
°C
°C
V
125
VDD
1
Vi
Applied voltage to all functional input pins and bidirectional pins 0
excluding LPClockIn, notRST and test control pins.
Virtc
fclk
Applied voltage to LPClockIn, notRST and test control pins
0
VDDrtc
V
ClockIn frequency
ClockIn frequency in TimesOneMode
16.5
36
MHz
MHz
2
Cl
Load capacitance per pin
50
pF
Table 17.2 Operating conditions
Notes
1 For a package junction to case thermal resistance of 14°C/W.
2 The nominal input clock frequency must be 16.368 MHz for the DSP module to function cor-
rectly with the GPS satellites.
97/116
ST20-GP1
DC specifications
Symbol Parameter
Min
Typical Max
Units Notes
VDD
Positive supply voltage during normal operation.
3.0
3.3
0
3.6
0.3
V
V
VDDoff
Positive supply voltage when device is off but real time -0.3
clock is running.
VDDrtc
Voltage at RTCVDD pin referred to GND.
3.0
3.3
0
3.6
0.3
V
VDDdiff VDD-VDDrtc during normal operation and notRST set to -0.3
V
1
1.
Vih
Input logic 1 for LPClockIn, notRST and test control pins. 2.0
VDDrtc + 0.5
VDD + 0.5
VDD + 0.5
V
Input logic 1 for all other inputs.
PIO pins.
2.0
2.4
Vil
Input logic 0 for all inputs.
-0.5
-10
-50
2.4
0
0.8
10
Iin
Input current to input pins.
µA
µA
V
Ioz
Off state digital output current.
Output logic 1
50
Vohdc
Voldc
Cin
VDD
0.4
10
2
3
Output logic 0
Input capacitance (input only pins).
Output capacitance and capacitance of bidirectional pins.
4
pF
pF
W
Cout
Pop
6
15
Operational power consumption under heavy device
activity. fclk of 16.368 MHz and SpeedSelect set to PLL
operation (x1). No external memory used.
0.5
0.8
4
4
Papp
Operational power consumption under ‘typical’ device
activity. fclk of 16.368 MHz and SpeedSelect set to PLL
operation (x2). External memory used.
0.75
0.16
1.1
W
Pstby
Prtc
Operational power during stand-by.
0.3
1
W
5
6
Operational power for the real time clock only, supplied
mW
through the RTCVDD pin.
Table 17.3 DC specification
Notes
1 This is the static specification to ensure low current.
2 Output current of 2mA.
3 Output current of -2mA.
4 Excludes power used to drive external loads. Includes operation of the 32 KHz watch crys-
tal oscillator.
5 Device operation suspended by use of the low power controller with VDD and RTCVDD
within specification. Frequency of system clock (fclk) is 16.368 MHz and frequency of low
power clock is 32768 Hz.
6 With RTCVDD within specification and VDD at 0 V. All inputs static except LowPower-
ClockIn and LowPowerClockOsc, frequency of low power clock 32768 Hz. All other
inputs must be in the range -0.1 to 0.1 V.
98/116
ST20-GP1
AC specifications
Symbol Parameter
Min
Typical Max
100 ms
Units
Notes
tvddr
Rise time of VDD during power up (measured 5 ns
1, 2
between 0.3 V and 2.7 V).
tvddf
Fall time of VDD during power down (measured 5 ns
100 ms
1, 2
between 2.7 V and 0.3 V).
Table 17.4 AC Specification
Notes
1 The maximum is only a guideline to ensure a low current consumption during the change in
VDD.
2 The transition need not be monotonic, providing that the notRST pin is forced low during
the whole period while the main VDD voltage is not within limits set in the DC operating
conditions.
99/116
ST20-GP1
18 GPS Performance
This chapter details the performance of a ST20-GP1 based GPS receiver.
Note that the performance is dependent on the quality of the user radio, antenna and software
used to track the signal and to calculate the resultant position.
18.1 Accuracy
18.1.1 Benign site
The accuracy performance of a GPS receiver is dependent on external factors, in particular the
deliberate degradation of the signal by the US DoD, known as Selective Availability (SA). This
results in an error specification of 100m.
If signal errors are corrected by differential GPS, the ST20-GP1 can achieve better than 1m
accuracy with 1-second rate corrections. Note that the ST20-GP1 supports the RTCA-SC159
provided corrections with no additional hardware.
For surveying use, the resolution of the counters used in the phase/frequency tracking allows
resolution down to 1mm.
Accuracy
Stand alone
with Selective Availability
without Selective Availability
< 100m
< 30m
Differential
< 1m
Surveying
< 1cm
Table 18.1 Accuracy performance
18.1.2 Under harsh conditions
Under harsh conditions, accuracy degrades due to:
•
•
•
noise on the weakened signal
reflected signals from buildings and cliffs
obstruction of satellites
The ST20-GP1 pays a 2 dB signal/noise ratio penalty by using 1-bit signal coding, there are then
no further losses in the signal processing hardware. The fast sampling rate, with both in-phase and
quadrature channels, results in the subsequent processing being 11 dB better, on a signal to noise
ratio, than earlier systems that sample at 2 MHz. Thus there is a 9 dB overall improvement.
100/116
ST20-GP1
18.2 Time to first fix
Time to
first fix
Condition
Receiver situation
autonomous
start
the receiver has no estimate of time/date/position and no recent almanac
90s
cold start
the receiver has estimated time/date/position and almanac
45s
warm start
obscuration
the receiver has estimated time/date/position and almanac and still valid ephemeris data 7s
the receiver has precise time (to µs level) as its calibrated clock is not stopped
1s
Table 18.2 Time to first fix
101/116
ST20-GP1
19 Timing specifications
19.1 EMI timings
The timings are based on a 50 pF load, and are taken at a threshold of 1.5 V.
Symbol Parameter
Min
-9.0
-11.0
-9.0
32.0
-9.0
-9.0
27.0
-6.0
Max
0.0
3.0
0.0
-
Units Notes
tCHAV
tCLSV
tCHSV
tRDVCH
Reference clock high to Address valid
ns
ns
ns
ns
ns
ns
ns
ns
Reference clock low to Strobe valid
Reference clock high to Strobe valid
Read Data valid to Reference clock high
tCHRDX Read Data hold after Reference clock high
tCHWDV Reference clock high to Write Data valid
-
2.0
-
tWVCH
tCHWX
MemWait valid to Reference clock high
MemWait hold after Reference clock high
-
Table 19.1 EMI cycle timings
Note: The ‘Reference clock’ used in the EMI timings is a virtual clock and is defined as the point at
which all data and address outputs are valid. This is designed to remove process dependent skews
from the datasheet description and highlight the dominant influence of address and data timings on
memory system design.
102/116
ST20-GP1
Reference clock
MemAddr1-19
tCHAV
tCHSV
tCLSV
notMemCE0-3
notMemOE0-3
notMemWB0-1
tCHRDX
tRDVCH
MemData0-15
(Read)
tCHWDV
MemData0-15
(Write)
tWVCH
tCHWX
MemWait
Figure 19.1 EMI timings
103/116
ST20-GP1
19.2 Link timings
Symbol
tJQr
Parameter
Min
Nom
Max
20
Units
ns
Notes
LinkOut rise time
LinkOut fall time
LinkIn rise time
LinkIn fall time
tJQf
10
ns
tJDr
20
ns
tJDf
20
ns
tJQJD
∆tJB
Buffered edge delay
Variation in tJQJD
0
ns
20 Mbits/s
10 Mbits/s
5 Mbits/s
3
ns
1
1
1
10
30
10
50
ns
ns
CLIZ
CLL
LinkIn capacitance
@ f=1MHz
pF
pF
LinkOut load capacitance
Notes
1 This is the variation in the total delay through buffers, transmission lines, differential receiv-
ers etc., caused by such things as short term variation in supply voltages and differences in
delays for rising and falling edges.
Table 19.2 Link timings
90%
LinkOut
10%
tJQr
tJQf
90%
10%
LinkIn
tJDr
tJDf
Figure 19.2 Link timings
1.5 V
LinkOut
Latest tJQJD
Earliest tJQJD
1.5 V
LinkIn
∆tJB
Figure 19.3 Buffered Link timings
104/116
ST20-GP1
19.3 Reset and Analyse timings
Symbol
tRHRL
tRHRL
tAHRH
tRLAL
Parameter
Min Nom Max
Units
ClockIn
ClockIn
ms
Notes
notRST pulse width low
8
1
3
1
CPUReset pulse width high
CPUAnalyse setup before CPUReset
CPUAnalyse hold after CPUReset end
ClockIn
Table 19.3 Reset and Analyse timings
notRST
tRSTHRSTL
CPUReset
tRHRL
tAHRH
tRHRL
tRLAL
CPUAnalyse
Figure 19.4 Reset and Analyse timings
105/116
ST20-GP1
19.4 ClockIn timings
Symbol
tDCLDCH
tDCHDCL
tDCr
Parameter
Min
18
Nom
Max
42.5
42.5
20
Units Notes
ClockIn pulse width low for PLL operation
ClockIn pulse width high for PLL operation
ClockIn rise time for PLL operation
ClockIn fall time for PLL operation
GPSIF valid before clock rising edge
GPSIF valid after clock rising edge
ns
ns
18
ns
ns
ns
ns
3
3
tDCf
20
tGDVCH
tCHGDX
20
0
Notes
1 Measured between corresponding points on consecutive falling edges.
2 Variation of individual falling edges from their nominal times.
3 Clock transitions must be monotonic within the range VIH to VIL (see Electrical Specifica-
tions).
Table 19.4 ClockIn timings
GPSIF
tGDVCH tCHGDX
2.0V
1.5V
0.8V
tDCLDCH
tDCHDCL
90%
10%
90%
10%
tDCf
tDCr
Figure 19.5 ClockIn timings
19.4.1 ClockIn frequency
Nominal ClockIn frequency is 16.36800 Mhz ±50 ppm tolerance. This tolerance relates to the GPS
system requirements and not for the device to function.
106/116
ST20-GP1
19.5 Parallel port timings
19.5.1 Dreq/Dack protocol
In this mode the two control pins PlinknotReq (Dreq) and PlinknotAck (Dack) are active low. The
initial (inactive) state of the two control wires is high.
Symbol Parameter
Min
Max Units
PLink is output tPALPDV PlinknotAck falling transition to PlinkData valid
tPAHDOX PlinkData hold time after rising edge of PlinknotAck
100
ns
ns
ns
ns
ns
ns
ns
ns
10
0
tPAHDOZ PlinkData output tristate time from PlinknotAck rising edge
PLink is input tPAHDIX PlinkData hold after PlinknotAck rising edge
tPALDIV PlinkData valid after PlinknotAck falling edge
90
20
PLink is input tPAHPRL PlinknotAck rising edge to succeeding PlinknotReq falling edge
0
or output
tPALPAH PlinknotAck low time
55
25
340
tPRLPAL Time between the input PlinknotReq falling and the output Plin-
knotAck falling
see
note 1
Table 19.5 Timings for Dreq/Dack protocol
Notes:
1 This will be a maximum of 200 ns if the port is already programmed either to accept another
byte or to write another byte and the port has the data available. In the extreme case for a
PLink output this value could be very large if the link has to wait for other external accesses
to complete before it can read the data to write out through the PLink.
tPAHPRL
tPRLPAL
PlinknotReq
(Dreq)
tPALPAH
PlinknotAck
(Dack)
tPAHDOX
tPALDOV
PlinkData0-7
(Output)
tPAHDOZ
tPALDIV
PlinkData0-7
(Input)
tPAHDIX
Figure 19.6 Byte-wide parallel port timings when using the Dreq/Dack protocol
107/116
ST20-GP1
19.5.2 Valid/Ack protocol
In this mode the two control pins PlinknotReq (Qack/Ivalid) and PlinknotAck (Qvalid/Iack) are
active high. The initial (inactive) state of the two control wires is low.
Symbol Parameter
Min
Max
Units
PLink is output
tPAHPRH PlinknotAck rising transition to PlinknotReq rising
tDOVPAH PlinkData0-7 setup time before rising edge of PlinknotAck
tPRHPAL PlinknotReq rising edge to PlinknotAck falling edge
tPALPRL PlinknotReq falling edge after PlinknotAck falling edge
0
0
0
0
0
ns
ns
ns
ns
ns
tPRLDOX PlinkData0-7 hold time after PlinknotReq falling edge
(i.e. before new data may be put onto bus)
PLink is input
tDIVPRH PlinkData setup time before PlinknotReq rising edge
tPAHDIX PlinkData hold after PlinknotAck rising edge
0
0
ns
ns
ns
ns
ns
ns
tPAHPRL PlinknotReq falling edge after PlinknotAck rising edge
tPRLPAH PlinknotReq falling edge to PlinknotAck rising edge
tPRLPAL PlinknotAck falling edge after PlinknotReq falling edge
tPALPRH PlinknotReq rising edge after PlinknotAck falling edge
0
0
40
0
300
Table 19.6 Timings for Valid/Ack protocol
ST20 Output
PlinknotAck
(Qvalid)
tPRHPAL
tPAHPRH
tPALPRL
PlinknotReq
(Qack)
tDOVPAH
tPRLDOX
PlinkData0-7
old data
valid data
ST20 Input
tPRLPAL
PlinknotReq
(Ivalid)
tPAHPRL
tPRLPAH
tPALPRH
PlinknotAck
(Iack)
tPAHDIX
PlinkData0-7
tDOVPRH
Figure 19.7 Byte-wide parallel port timings when using the Valid/Ack protocol
108/116
ST20-GP1
19.5.3 Direct DMA protocol
In this mode PlinknotAck is active high. The initial (inactive) state of the pin is low.
Symbol Parameter
16.4 Mhz
32.7 Mhz
Units
Min
Max
Min
Max
PLink is output
PLink is input
tPALDOX PlinkData hold after PlinknotAck
330
100
0
160
40
0
ns
ns
ns
ns
falling edge
tDOVPAL PlinkData valid to PlinknotAck fall-
ing transition
tPALDIX PlinkData hold after PlinknotAck
falling edge
tDIVPAL PlinkData valid to PlinknotAck fall-
100
70
ing transition
PLink is input or
output
tPAHPAL PlinknotAck high time
tPALPAH PlinknotAck low time
220
220
270
270
100
100
140
140
ns
ns
Table 19.7 Timings for Direct mode
tPALPAH
tPALDOX
PlinknotAck
tPAHPAL
tDOVPAL
PlinkData0-7
(Output)
tPALDIX
tDIVPAL
PlinkData0-7
(Input)
Figure 19.8 Byte-wide parallel port timings when using the Direct DMA protocol
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ST20-GP1
20 Pin list
Signals names are prefixed by not if they are active low, otherwise they are active high.
Supplies
Pin
In/Out
Function
Power supply
Ground
VDD
GND
Table 20.1 ST20-GP1 supply pins
Clocks
Pin
In/Out
in
Function
LowPowerClockIn
LowPowerClockOsc
LowPowerStatus
notWdReset
RTCVDD
Low power input clock
Low power clock oscillator
Low power status
in/out
out
out
Watchdog timer reset
Real time clock supply
in
Table 20.2 ST20-GP1 low power controller and real time clock pins
System services
Pin
In/Out
in
Function
ClockIn
System input clock – PLL or TimesOneMode
SpeedSpeed0-1
in
Speed selectors
Reset
notRST
in
CPUReset
CPUAnalyse
ErrorOut
in
System reset
Error analysis
Error indicator
in
out
Table 20.3 ST20-GP1 system services pins
Links
Pin
In/Out
in
Function
LinkIn
LinkOut
Serial data input channel
Serial data output channel
out
Table 20.4 ST20-GP1 link pins
Interrupts
Pin
In/Out
Function
Interrupt0-1
in
Interrupts
Table 20.5 ST20-GP1 interrupt pins
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ST20-GP1
Memory
Pin
In/Out
out
Function
MemAddr1-19
MemData0-15
Address bus
in/out
Data bus. Data0 is the least significant bit (LSB) and
Data15 is the most significant bit (MSB).
MemWait
in
Memory cycle extender
notMemOE0-3
notMemCE0-3
notMemWB0-1
BootSource0-1
out
out
out
in
Output enable strobes – one per bank
Chip enable strobes – one per bank
Used as write strobe, or MemAddr0 on 8-bit bus.
Boot from ROM or from link
Table 20.6 ST20-GP1 memory pins
UART
Pin
In/Out
out
Function
TXD0-1
RXD0-1
UART serial data output
UART serial data input
in
Table 20.7 ST20-GP1 UART pins
Parallel IO
Pin
In/Out
Function
PIO0-5
in/out
PIO
Table 20.8 ST20-GP1 parallel IO pins
Byte wide parallel port
Pin
In/Out
in/out
in
Function
PlinkData0-7
PlinknotReq
PlinknotAck
PlinkOut
Bidirectional data bus
Data transfer request
Data transfer acknowledge
out
out
Controls external buffers. When high signals the PLink is
outputting.
Table 20.9 ST20-GP1 byte wide parallel port pins
Application specific
Pin
In/Out
Function
GPSIF
in
GPS IF input
Table 20.10 ST20-GP1 application specific pins
Miscellaneous
Pin
In/Out
Function
ConnectToGND
Must be connected to GND
Table 20.11 ST20-GP1 miscellaneous pins
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ST20-GP1
21 Package specifications
The ST20-GP1 is available in a 100 pin plastic quad flat pack (PQFP) package.
21.1 ST20-GP1 package pinout
Figure 21.1 ST20-GP1 100 pin PQFP package pinout
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ST20-GP1
21.2 100 pin PQFP package dimensions
REF.
CONTROL DIM. mm
MIN
ALTERNATIVE DIM. INCHES
MIN
NOTES
A
A1
A2
B
-
-
3.400
-
-
0.134
-
0.100
2.540
0.220
0.130
-
-
3.050
0.380
0.230
24.150
20.100
-
0.004
0.096
0.009
0.005
0.904
0.783
-
-
2.800
0.110
-
0.120
0.015
0.009
0.951
0.791
-
-
-
C
-
D
22.950
-
-
D1
D3
E
19.900
20.000
18.850
-
0.787
0.742
-
-
REF
16.950
18.150
14.100
-
0.667
0.547
-
0.715
0.555
-
E1
E3
e
13.900
14.000
12.350
0.650
-
0.551
0.486
0.026
-
-
REF
BSC
-
-
-
-
G
-
0.100
7°
-
0.004
7°
K
0°
-
0°
-
L
0.650
0.800
0.580
0.830
0.950
-
0.026
-
0.031
0.23
0.033
0.037
-
Zd
Ze
-
-
REF
REF
-
-
-
Notes
1 Lead finish to be 60 Sn/40 Pb solder plate.
2 Maximum lead displacement from the notional centre line will be no greater than
±0.125 mm.
Table 21.1 100 pin PQFP package dimensions
113/116
ST20-GP1
Figure 21.2 100 pin PQFP package dimensions
114/116
ST20-GP1
22 Device ID
The identification code for the ST20-GP1 is #m5191011, where m is a manufacturing revision
number reserved by SGS-THOMSON. See Table 22.1.
bit 31
bit 0
SGS-THOMSON
manufacturers id
a
b
Mask rev
reserved
ST20 family
Variant
0 1 0 1 0 0 0 1 1 0 0 1 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 1
5
1
9
1
0
1
1
Table 22.1 Identification code
a. 0 indicates SGS-THOMSON part, 1 indicates customer part.
b. Defined as 1 in IEEE 1149.1 standard.
The identification code is returned by the lddevid instruction, see Table 6.4.
23 Ordering information
Device
Package
ST20GP1X33S
100 pin plastic quad flatpack (PQFP)
For further information contact your local SGS-THOMSON sales office.
115/116
ST20-GP1
Information furnished is believed to be accurate and reliable. However, SGS-THOMSON Microelectronics assumes no responsibility for the conse-
quences of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is
granted by implication or otherwise under any patent or patent rights of SGS-THOMSON Microelectronics. Specifications mentioned in this publication
are subject to change without notice. This publication supersedes and replaces all information previously supplied. SGS-THOMSON Microelectronics
products are not authorized for use as critical components in life support devices or systems without express written approval of SGS-THOMSON
Microelectronics.
© 1996 SGS-THOMSON Microelectronics - All Rights Reserved
IMS and DS-Link are trademarks of SGS-THOMSON Microelectronics Limited.
is a registered trademark of the SGS-THOMSON Microelectronics Group.
SGS-THOMSON Microelectronics GROUP OF COMPANIES
Australia - Brazil - Canada - China - France - Germany - Hong Kong - Italy - Japan - Korea - Malaysia - Malta - Morocco -
The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A.
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116
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